fix(cli): harden native service manager preflight

.changeset/doctor-native-service-context.md

@@ -2,4 +2,4 @@
 "@jmfederico/pi-web": patch
 ---
 
-Validate install and doctor service requirements in the real systemd or launchd manager context before changing native services, with plan-specific PATH guidance and safe probe cleanup. Thanks to @blain3white for the original report, reproduction, and diagnosis.
+Validate install and doctor service requirements in the real systemd or launchd manager context before changing native services, with plan-specific PATH guidance and safe probe cleanup. Thanks to @blain3white for the original report, reproduction, and root-cause analysis.

README.md

@@ -64,7 +64,7 @@ pi-web version
 pi-web uninstall
 ```
 
-`pi-web install` validates the exact production or development service plan inside the native user-service manager before changing config or replacing services. `pi-web doctor` repeats manager-context diagnostics, labels prospective production checks when an installed command strategy cannot be reconstructed, and keeps general shell/Pi/npm readiness separate from service-start requirements.
+`pi-web install` validates the safely verifiable requirements of the exact production or development service plan inside the native user-service manager before changing config or replacing services; arbitrary configured command overrides are preserved but not executed by preflight. `pi-web doctor` repeats manager-context diagnostics, labels prospective production checks when an installed command strategy cannot be reconstructed, and keeps general shell/Pi/npm readiness separate from service-start requirements.
 
 For more install options, including one-line install, Pi package install, WSL/manual usage, and remote access, see the [installation guide](https://pi-web.dev/install).
 

docs/install.html

@@ -114,8 +114,9 @@
                 <strong>Important PATH detail:</strong>
                 PI WEB services run through a non-interactive login shell with <code>-lc</code>. Setup that only lives in
                 interactive shell files or prompt hooks may not be visible to the systemd or launchd manager. The installer
-                probes the exact candidate plan in that manager context before changing config or replacing services; run
-                <code>pi-web doctor</code> later to repeat plan-specific diagnostics.
+                probes the safely verifiable requirements of the exact candidate plan in that manager context before changing
+                config or replacing services. Arbitrary configured command overrides are preserved but not executed by
+                preflight; run <code>pi-web doctor</code> later to repeat plan-specific diagnostics.
               </div>
             </section>
 

src/cli.test.ts

@@ -7,6 +7,7 @@ import {
   doctorExitCode,
   isCliEntrypoint,
   launchdRuntimeDetails,
+  regularFileExists,
   serviceBackendForPlatform,
 } from "./cli.js";
 
@@ -53,6 +54,19 @@ describe("native-service doctor CLI contracts", () => {
     expect(doctorExitCode(true, true, false)).toBe(1);
   });
 
+  it("accepts only regular files as bundled entrypoints", () => {
+    const dir = mkdtempSync(join(tmpdir(), "pi-web-entrypoint-test-"));
+    try {
+      const file = join(dir, "entrypoint.js");
+      writeFileSync(file, "export {};\n");
+      expect(regularFileExists(file)).toBe(true);
+      expect(regularFileExists(dir)).toBe(false);
+      expect(regularFileExists(join(dir, "missing.js"))).toBe(false);
+    } finally {
+      rmSync(dir, { recursive: true, force: true });
+    }
+  });
+
   it("surfaces launchd last exit code 127 in service status", () => {
     expect(launchdRuntimeDetails("state = exited\nlast exit code = 127\n")).toEqual({
       state: "exited",

src/cli.ts

@@ -1,6 +1,6 @@
 #!/usr/bin/env node
 import { spawnSync } from "node:child_process";
-import { existsSync, readFileSync, realpathSync } from "node:fs";
+import { existsSync, readFileSync, realpathSync, statSync } from "node:fs";
 import { mkdir, rm, writeFile } from "node:fs/promises";
 import { homedir, userInfo } from "node:os";
 import { basename, dirname, join, resolve } from "node:path";
@@ -10,6 +10,7 @@ import { packageVersion, printPiWebVersionReport } from "./piWebVersionReport.js
 import { checkNodePtyDarwinSpawnHelper, formatNodePtyDarwinSpawnHelperCheck } from "./server/diagnostics/nodePtySpawnHelper.js";
 import {
   installNativeServiceCandidate,
+  nativeServiceInstallFailureNeedsPathAdvice,
   type NativeServiceInstallCandidate,
   type NativeServiceInstallFailure,
 } from "./nativeServices/serviceInstall.js";
@@ -218,6 +219,10 @@ function packageEntrypointPath(name: "server" | "sessiond"): string {
   return join(packageRootPath(), "dist", "server", name === "server" ? "index.js" : "sessiond.js");
 }
 
+export function regularFileExists(path: string): boolean {
+  return existsSync(path) && statSync(path).isFile();
+}
+
 function detectServiceShell(): NativeServiceShell {
   const userShell = userInfo().shell ?? undefined;
   const envShell = process.env["SHELL"]?.trim();
@@ -660,15 +665,18 @@ async function install(args: string[]): Promise<void> {
   console.log(`Service shell: ${describeServiceShell()}`);
   const result = await installNativeServiceCandidate(candidate, {
     probe: createNativeServiceAuthoritativeProbe(),
-    fileExists: existsSync,
+    fileExists: regularFileExists,
     writeInitialConfig: () => writeInitialConfig(options, configPath),
     replaceServices: installNativeServices,
   });
   if (!result.ok) {
     printNativeServiceInstallFailure(result.failure);
-    printPathSetupAdvice();
+    if (nativeServiceInstallFailureNeedsPathAdvice(result.failure)) printPathSetupAdvice();
     throw new Error("Install preflight checks failed without changing config or services. Fix the failure above, then run `pi-web doctor` for more detail.");
   }
+  for (const service of result.plan.services.filter((item) => item.strategy.kind === "configured-override")) {
+    console.log(`! ${service.description} uses a configured command override; preflight did not execute that arbitrary command.`);
+  }
 
   console.log(`\nPI WEB ${options.mode} services are installed and starting.`);
   console.log(`Config: ${configPath}`);
@@ -893,7 +901,7 @@ function nativeServiceDoctorTarget(backend: ServiceBackend): NativeServiceDoctor
 async function printNativeServiceDoctorChecks(backend: ServiceBackend): Promise<NativeServiceDoctorReport> {
   const result = await runNativeServiceDoctor(nativeServiceDoctorTarget(backend), {
     probe: createNativeServiceAuthoritativeProbe(),
-    fileExists: existsSync,
+    fileExists: regularFileExists,
   });
   const report = formatNativeServiceDoctorResult(result);
   for (const line of report.lines) console.log(line);
@@ -994,11 +1002,11 @@ async function doctor(): Promise<void> {
   }
 
   const nativeServicePlanOk = nativeServiceReport?.ok ?? true;
-  const pathFailure = !generalReadinessOk || nativeServiceReport?.failureKind === "requirements";
+  const pathFailure = !generalReadinessOk || nativeServiceReport?.pathAdviceRecommended === true;
   if (pathFailure) {
     console.log("\nIf a command works in your terminal but fails in the service-manager check, compare the caller and manager contexts above.");
-    const adviceShell = nativeServiceReport?.failureKind === "requirements" && nativeServiceReport.plan !== null
-      ? nativeServiceReport.plan.shell
+    const adviceShell = nativeServiceReport?.pathAdviceRecommended === true && nativeServiceReport.adviceShell !== null
+      ? nativeServiceReport.adviceShell
       : detectServiceShell();
     printPathSetupAdvice(adviceShell);
   }

src/nativeServices/serviceDoctor.test.ts

@@ -98,13 +98,39 @@ describe("installed native-service mode and definition inspection", () => {
     });
   });
 
+  it("reconstructs escaped systemd paths, substitutions, and line controls exactly", () => {
+    const plan = createDevelopmentNativeServicePlan({
+      backend: { kind: "systemd", label: "systemd" },
+      shell: {
+        name: "zsh",
+        executable: "/shell $HOME/%h/zsh",
+        source: "detected",
+        detectedExecutable: "/shell $HOME/%h/zsh",
+      },
+      environment: { PI_WEB_CONFIG: "/config/%h\nnext" },
+      workingDirectory: "/checkout %h\nnext",
+      packageJsonPath: "/checkout %h\nnext/package.json",
+    });
+
+    expect(inspectInstalledDevelopmentServiceInput(plan.backend, renderedDefinitions(plan))).toEqual({
+      ok: true,
+      value: {
+        backend: plan.backend,
+        shell: plan.shell,
+        environment: plan.services[0]?.environment,
+        workingDirectory: "/checkout %h\nnext",
+        packageJsonPath: "/checkout %h\nnext/package.json",
+      },
+    });
+  });
+
   it("inspects legacy systemd definitions without /usr/bin/env or quoted working directories", () => {
     const plan = developmentPlan("systemd");
     const definitions = renderedDefinitions(plan).map((definition) => ({
       ...definition,
       contents: definition.contents
         .replace("ExecStart=/usr/bin/env ", "ExecStart=")
-        .replace('WorkingDirectory="/checkout with space"', "WorkingDirectory=/checkout with space"),
+        .replace("WorkingDirectory=/checkout\\x20with\\x20space", "WorkingDirectory=/checkout with space"),
     }));
 
     expect(inspectInstalledDevelopmentServiceInput(plan.backend, definitions)).toMatchObject({
@@ -113,6 +139,80 @@ describe("installed native-service mode and definition inspection", () => {
     });
   });
 
+  it("rejects quoted systemd working directories that the manager treats as non-absolute", () => {
+    const plan = developmentPlan("systemd");
+    const definitions = renderedDefinitions(plan).map((definition) => ({
+      ...definition,
+      contents: definition.contents.replace(
+        "WorkingDirectory=/checkout\\x20with\\x20space",
+        'WorkingDirectory="/checkout with space"',
+      ),
+    }));
+
+    const inspection = inspectInstalledDevelopmentServiceInput(plan.backend, definitions);
+    expect(inspection.ok).toBe(false);
+    if (inspection.ok) throw new Error("Expected quoted working directory inspection to fail");
+    expect(inspection.message).toContain("invalid quoted working directory");
+  });
+
+  it("rejects unconsumed systemd environment syntax rather than checking a different context", () => {
+    const plan = developmentPlan("systemd");
+    const definitions = renderedDefinitions(plan).map((definition) => ({
+      ...definition,
+      contents: definition.contents.replace("[Service]\n", "[Service]\nEnvironment=PATH=/custom/bin\n"),
+    }));
+
+    const inspection = inspectInstalledDevelopmentServiceInput(plan.backend, definitions);
+    expect(inspection.ok).toBe(false);
+    if (inspection.ok) throw new Error("Expected systemd environment inspection to fail");
+    expect(inspection.message).toContain("environment entry");
+  });
+
+  it.each([
+    'Environment="PI_WEB_CONFIG=/config" "PATH=/broken"',
+    "EnvironmentFile=/tmp/pi-web.env",
+  ])("rejects noncanonical systemd environment context: %s", (directive) => {
+    const plan = developmentPlan("systemd");
+    const definitions = renderedDefinitions(plan).map((definition) => ({
+      ...definition,
+      contents: definition.contents.replace("[Service]\n", `[Service]\n${directive}\n`),
+    }));
+
+    expect(inspectInstalledDevelopmentServiceInput(plan.backend, definitions).ok).toBe(false);
+  });
+
+  it("rejects duplicate systemd ExecStart directives", () => {
+    const plan = developmentPlan("systemd");
+    const definitions = renderedDefinitions(plan).map((definition) => ({
+      ...definition,
+      contents: definition.contents.replace(
+        "Restart=no",
+        'ExecStart=/usr/bin/env "/bin/zsh" -lc "exec true"\nRestart=no',
+      ),
+    }));
+
+    const inspection = inspectInstalledDevelopmentServiceInput(plan.backend, definitions);
+    expect(inspection.ok).toBe(false);
+    if (inspection.ok) throw new Error("Expected duplicate ExecStart inspection to fail");
+    expect(inspection.message).toContain("exactly one recognized ExecStart");
+  });
+
+  it("rejects malformed launchd environment dictionaries rather than dropping entries", () => {
+    const plan = developmentPlan("launchd");
+    const definitions = renderedDefinitions(plan).map((definition) => ({
+      ...definition,
+      contents: definition.contents.replace(
+        "  </dict>\n  <key>RunAtLoad</key>",
+        "    <key>BROKEN</key>\n    <integer>1</integer>\n  </dict>\n  <key>RunAtLoad</key>",
+      ),
+    }));
+
+    const inspection = inspectInstalledDevelopmentServiceInput(plan.backend, definitions);
+    expect(inspection.ok).toBe(false);
+    if (inspection.ok) throw new Error("Expected launchd environment inspection to fail");
+    expect(inspection.message).toContain("environment dictionary");
+  });
+
   it("rejects a modified development command rather than claiming to check the installed plan", () => {
     const plan = developmentPlan("systemd");
     const definitions = renderedDefinitions(plan);
@@ -168,6 +268,31 @@ describe("native-service doctor planning and reporting", () => {
     );
   });
 
+  it("does not recommend PATH changes for checkout metadata failures", async () => {
+    const plan = developmentPlan("systemd");
+    const inspected = inspectInstalledDevelopmentServiceInput(plan.backend, renderedDefinitions(plan));
+    if (!inspected.ok) throw new Error(inspected.message);
+    const result = await runNativeServiceDoctor(
+      { kind: "installed-development", input: inspected.value },
+      {
+        probe: {
+          run: (request) => Promise.resolve({
+            kind: "completed",
+            outcomes: request.prerequisites.map((prerequisite) => ({
+              prerequisiteId: prerequisite.id,
+              status: prerequisite.kind === "package-scripts" ? "unsatisfied" as const : "satisfied" as const,
+              detail: prerequisite.kind === "package-scripts" ? "scripts missing" : null,
+            })),
+          }),
+        },
+        fileExists: () => true,
+      },
+    );
+    const report = formatNativeServiceDoctorResult(result);
+
+    expect(report).toMatchObject({ ok: false, failureKind: "requirements", pathAdviceRecommended: false });
+  });
+
   it("labels a production check as prospective and reports manager-context requirements", async () => {
     const target: NativeServiceDoctorTarget = {
       kind: "prospective-production",
@@ -190,6 +315,22 @@ describe("native-service doctor planning and reporting", () => {
     ]));
   });
 
+  it("retains the installed production shell when resolution fails before a plan exists", async () => {
+    const result = await runNativeServiceDoctor(
+      { kind: "prospective-production", input: productionInput(), reason: "installed strategy is unknown" },
+      { probe: probeWithStatus("unsatisfied"), fileExists: () => false },
+    );
+    const report = formatNativeServiceDoctorResult(result);
+
+    expect(report).toMatchObject({
+      ok: false,
+      failureKind: "requirements",
+      plan: null,
+      adviceShell: shell,
+      pathAdviceRecommended: true,
+    });
+  });
+
   it("preserves configured overrides as unverified and does not probe arbitrary commands", async () => {
     let calls = 0;
     const result = await runNativeServiceDoctor(
@@ -201,7 +342,7 @@ describe("native-service doctor planning and reporting", () => {
     );
     const report = formatNativeServiceDoctorResult(result);
 
-    expect(calls).toBe(0);
+    expect(calls).toBe(1);
     expect(report.ok).toBe(true);
     expect(report.lines.join("\n")).toContain("does not execute arbitrary configured commands");
   });

src/nativeServices/serviceDoctor.ts

@@ -1,6 +1,7 @@
 import { basename, join } from "node:path";
 import {
   createDevelopmentNativeServicePlan,
+  nativeServicePrerequisiteNeedsPathAdvice,
   resolveProductionNativeServicePlan,
   validateNativeServicePlan,
   type DevelopmentNativeServicePlanInput,
@@ -49,6 +50,7 @@ export type NativeServiceDoctorTarget =
 interface NativeServiceDoctorScope {
   kind: "installed-development" | "prospective-production";
   reason: string | null;
+  shell: NativeServiceShell;
 }
 
 export type NativeServiceDoctorResult =
@@ -73,6 +75,8 @@ export interface NativeServiceDoctorReport {
   failureKind: "none" | "requirements" | "infrastructure" | "inspection";
   lines: readonly string[];
   plan: NativeServicePlan | null;
+  adviceShell: NativeServiceShell | null;
+  pathAdviceRecommended: boolean;
   failedPrerequisites: readonly NativeServicePrerequisite[];
 }
 
@@ -153,8 +157,8 @@ export async function runNativeServiceDoctor(
   if (target.kind === "inspection-failure") return target;
 
   const scope: NativeServiceDoctorScope = target.kind === "installed-development"
-    ? { kind: target.kind, reason: null }
-    : { kind: target.kind, reason: target.reason };
+    ? { kind: target.kind, reason: null, shell: target.input.shell }
+    : { kind: target.kind, reason: target.reason, shell: target.input.shell };
   let plan: NativeServicePlan;
   if (target.kind === "installed-development") {
     plan = createDevelopmentNativeServicePlan(target.input);
@@ -180,6 +184,8 @@ export function formatNativeServiceDoctorResult(result: NativeServiceDoctorResul
         "  Run `pi-web install` or `pi-web install --dev` to replace mixed, partial, or outdated service definitions.",
       ],
       plan: null,
+      adviceShell: null,
+      pathAdviceRecommended: false,
       failedPrerequisites: [],
     };
   }
@@ -205,6 +211,9 @@ export function formatNativeServiceDoctorResult(result: NativeServiceDoctorResul
       failureKind: infrastructure ? "infrastructure" : "requirements",
       lines,
       plan: null,
+      adviceShell: result.scope.shell,
+      pathAdviceRecommended: !infrastructure
+        && result.failures.some((failure) => failure.kind === "executable-unavailable"),
       failedPrerequisites: [],
     };
   }
@@ -215,7 +224,15 @@ export function formatNativeServiceDoctorResult(result: NativeServiceDoctorResul
   }
   if (result.validation.ok) {
     lines.push("✓ All verifiable native-service plan requirements are satisfied in the service-manager context.");
-    return { ok: true, failureKind: "none", lines, plan: result.plan, failedPrerequisites: [] };
+    return {
+      ok: true,
+      failureKind: "none",
+      lines,
+      plan: result.plan,
+      adviceShell: result.plan.shell,
+      pathAdviceRecommended: false,
+      failedPrerequisites: [],
+    };
   }
 
   const failedPrerequisites: NativeServicePrerequisite[] = [];
@@ -236,6 +253,9 @@ export function formatNativeServiceDoctorResult(result: NativeServiceDoctorResul
     failureKind: infrastructure ? "infrastructure" : "requirements",
     lines,
     plan: result.plan,
+    adviceShell: result.plan.shell,
+    pathAdviceRecommended: !infrastructure
+      && failedPrerequisites.some(nativeServicePrerequisiteNeedsPathAdvice),
     failedPrerequisites,
   };
 }
@@ -275,33 +295,85 @@ function parseConsistentDefinitions(
   return { ok: true, value: parsed };
 }
 
+interface ParsedSystemdDirective {
+  name: string;
+  value: string;
+}
+
+function systemdServiceDirectives(contents: string): ParsedSystemdDirective[] | undefined {
+  const allowed = new Set(["Type", "WorkingDirectory", "Environment", "ExecStart", "Restart", "RestartSec"]);
+  const directives: ParsedSystemdDirective[] = [];
+  let inServiceSection = false;
+  let foundServiceSection = false;
+  for (const line of contents.split(/\r?\n/u)) {
+    const trimmed = line.trim();
+    if (/^\[[^\]]+\]$/u.test(trimmed)) {
+      inServiceSection = trimmed === "[Service]";
+      foundServiceSection ||= inServiceSection;
+      continue;
+    }
+    if (!inServiceSection || trimmed === "" || trimmed.startsWith("#") || trimmed.startsWith(";")) continue;
+    const match = /^\s*([A-Za-z][A-Za-z0-9]*)=(.*)$/u.exec(line);
+    const name = match?.[1];
+    const value = match?.[2];
+    if (name === undefined || value === undefined || !allowed.has(name)) return undefined;
+    directives.push({ name, value });
+  }
+  return foundServiceSection ? directives : undefined;
+}
+
 function parseSystemdDefinition(
   definition: InstalledNativeServiceDefinition,
 ): InstalledNativeServiceInspection<ParsedServiceDefinition> {
-  const execStart = /^ExecStart=(?:\/usr\/bin\/env )?(.+?) -lc (.+)$/mu.exec(definition.contents);
-  if (execStart?.[1] === undefined || execStart[2] === undefined) {
-    return { ok: false, message: `Installed ${definition.id} systemd unit has an unrecognized ExecStart.` };
+  const directives = systemdServiceDirectives(definition.contents);
+  if (directives === undefined) {
+    return { ok: false, message: `Installed ${definition.id} systemd unit has unrecognized service directives.` };
   }
-  const shell = installedShell(execStart[1]);
+  const execStarts = directives.filter((directive) => directive.name === "ExecStart");
+  const execStart = execStarts.length === 1
+    ? /^(?:\/usr\/bin\/env )?(.+?) -lc (.+)$/u.exec(execStarts[0]?.value ?? "")
+    : null;
+  if (execStart?.[1] === undefined || execStart[2] === undefined) {
+    return { ok: false, message: `Installed ${definition.id} systemd unit must have exactly one recognized ExecStart.` };
+  }
+  const shellExecutable = parseSystemdExecArgument(execStart[1]);
+  if (shellExecutable === undefined) {
+    return { ok: false, message: `Installed ${definition.id} systemd unit has an unrecognized login shell argument.` };
+  }
+  const shell = installedShell(shellExecutable);
   if (!shell.ok) return shell;
-  const shellCommand = parseShellQuotedValue(shell.value.name, execStart[2]);
+  const shellCommand = parseSystemdShellCommand(shell.value.name, execStart[2]);
   if (shellCommand === undefined) {
     return { ok: false, message: `Installed ${definition.id} systemd unit has an unrecognized shell command.` };
   }
 
   const environment: Record<string, string> = {};
-  for (const match of definition.contents.matchAll(/^Environment="((?:\\.|[^"])*)"$/gmu)) {
-    const assignment = systemdUnescape(match[1] ?? "");
-    const separator = assignment.indexOf("=");
-    if (separator <= 0) return { ok: false, message: `Installed ${definition.id} systemd unit has a malformed environment entry.` };
-    environment[assignment.slice(0, separator)] = assignment.slice(separator + 1);
+  for (const directive of directives.filter((item) => item.name === "Environment")) {
+    const rawValue = directive.value;
+    if (!/^"(?:\\.|[^"])*"$/u.test(rawValue)) {
+      return { ok: false, message: `Installed ${definition.id} systemd unit has an unrecognized environment entry.` };
+    }
+    const assignment = parseSystemdDirectiveValue(rawValue);
+    const separator = assignment?.indexOf("=") ?? -1;
+    const key = assignment?.slice(0, separator) ?? "";
+    if (separator <= 0 || Object.hasOwn(environment, key)) {
+      return { ok: false, message: `Installed ${definition.id} systemd unit has a malformed environment entry.` };
+    }
+    environment[key] = assignment?.slice(separator + 1) ?? "";
   }
 
-  const workingDirectoryMatch = /^WorkingDirectory=(.+)$/mu.exec(definition.contents);
-  const workingDirectory = workingDirectoryMatch?.[1] === undefined
+  const workingDirectories = directives.filter((directive) => directive.name === "WorkingDirectory");
+  if (workingDirectories.length > 1) {
+    return { ok: false, message: `Installed ${definition.id} systemd unit has duplicate working directories.` };
+  }
+  const rawWorkingDirectory = workingDirectories[0]?.value;
+  if (rawWorkingDirectory?.startsWith('"') === true || rawWorkingDirectory?.startsWith("'") === true) {
+    return { ok: false, message: `Installed ${definition.id} systemd unit has an invalid quoted working directory.` };
+  }
+  const workingDirectory = rawWorkingDirectory === undefined
     ? null
-    : parseSystemdValue(workingDirectoryMatch[1]);
-  if (workingDirectoryMatch !== null && workingDirectory === undefined) {
+    : parseSystemdDirectiveValue(rawWorkingDirectory);
+  if (workingDirectories.length === 1 && workingDirectory === undefined) {
     return { ok: false, message: `Installed ${definition.id} systemd unit has a malformed working directory.` };
   }
 
@@ -314,25 +386,42 @@ function parseSystemdDefinition(
 function parseLaunchdDefinition(
   definition: InstalledNativeServiceDefinition,
 ): InstalledNativeServiceInspection<ParsedServiceDefinition> {
-  const argumentsBlock = /<key>ProgramArguments<\/key>\s*<array>([\s\S]*?)<\/array>/u.exec(definition.contents)?.[1];
-  if (argumentsBlock === undefined) {
-    return { ok: false, message: `Installed ${definition.id} LaunchAgent has no ProgramArguments array.` };
-  }
-  const arguments_ = [...argumentsBlock.matchAll(/<string>([\s\S]*?)<\/string>/gu)].map((match) => xmlUnescape(match[1] ?? ""));
-  if (arguments_.length !== 4 || arguments_[0] !== "/usr/bin/env" || arguments_[2] !== "-lc") {
+  const argumentsMatches = [...definition.contents.matchAll(/<key>ProgramArguments<\/key>\s*<array>([\s\S]*?)<\/array>/gu)];
+  const arguments_ = argumentsMatches.length === 1
+    ? parseXmlStringSequence(argumentsMatches[0]?.[1] ?? "")
+    : undefined;
+  if (arguments_?.length !== 4 || arguments_[0] !== "/usr/bin/env" || arguments_[2] !== "-lc") {
     return { ok: false, message: `Installed ${definition.id} LaunchAgent has unrecognized ProgramArguments.` };
   }
   const shell = installedShell(arguments_[1] ?? "");
   if (!shell.ok) return shell;
 
-  const environment: Record<string, string> = {};
-  const environmentBlock = /<key>EnvironmentVariables<\/key>\s*<dict>([\s\S]*?)<\/dict>/u.exec(definition.contents)?.[1];
-  if (environmentBlock !== undefined) {
-    for (const match of environmentBlock.matchAll(/<key>([\s\S]*?)<\/key>\s*<string>([\s\S]*?)<\/string>/gu)) {
-      environment[xmlUnescape(match[1] ?? "")] = xmlUnescape(match[2] ?? "");
-    }
+  const environmentMatches = [...definition.contents.matchAll(/<key>EnvironmentVariables<\/key>\s*<dict>([\s\S]*?)<\/dict>/gu)];
+  const environmentKeyCount = [...definition.contents.matchAll(/<key>EnvironmentVariables<\/key>/gu)].length;
+  if (environmentMatches.length > 1 || environmentKeyCount !== environmentMatches.length) {
+    return { ok: false, message: `Installed ${definition.id} LaunchAgent has a malformed environment dictionary.` };
+  }
+  const environment = environmentMatches.length === 0
+    ? {}
+    : parseXmlStringDictionary(environmentMatches[0]?.[1] ?? "");
+  if (environment === undefined) {
+    return { ok: false, message: `Installed ${definition.id} LaunchAgent has a malformed environment dictionary.` };
+  }
+
+  const contentsWithoutEnvironment = environmentMatches[0]?.[0] === undefined
+    ? definition.contents
+    : definition.contents.replace(environmentMatches[0][0], "");
+  const workingDirectoryMatches = [...contentsWithoutEnvironment.matchAll(/<key>WorkingDirectory<\/key>\s*<string>([\s\S]*?)<\/string>/gu)];
+  const workingDirectoryKeyCount = [...contentsWithoutEnvironment.matchAll(/<key>WorkingDirectory<\/key>/gu)].length;
+  if (workingDirectoryMatches.length > 1 || workingDirectoryKeyCount !== workingDirectoryMatches.length) {
+    return { ok: false, message: `Installed ${definition.id} LaunchAgent has a malformed working directory.` };
+  }
+  const workingDirectory = workingDirectoryMatches[0]?.[1] === undefined
+    ? null
+    : xmlUnescapeStrict(workingDirectoryMatches[0][1]);
+  if (workingDirectoryMatches.length === 1 && workingDirectory === undefined) {
+    return { ok: false, message: `Installed ${definition.id} LaunchAgent has a malformed working directory.` };
   }
-  const workingDirectory = launchdString(definition.contents, "WorkingDirectory");
 
   return {
     ok: true,
@@ -340,7 +429,7 @@ function parseLaunchdDefinition(
       id: definition.id,
       shell: shell.value,
       environment,
-      workingDirectory,
+      workingDirectory: workingDirectory ?? null,
       shellCommand: arguments_[3] ?? "",
     },
   };
@@ -357,31 +446,87 @@ function installedShell(executable: string): InstalledNativeServiceInspection<Na
   };
 }
 
-function parseSystemdValue(value: string): string | undefined {
-  if (!value.startsWith('"') && !value.endsWith('"')) return value;
-  if (!value.startsWith('"') || !value.endsWith('"')) return undefined;
-  return systemdUnescape(value.slice(1, -1));
+function parseSystemdExecArgument(value: string): string | undefined {
+  const decoded = parseSystemdEscapedValue(value);
+  return decoded === undefined ? undefined : decodeSystemdSubstitutions(decoded, true);
 }
 
-function systemdUnescape(value: string): string {
+function parseSystemdDirectiveValue(value: string): string | undefined {
+  const decoded = parseSystemdEscapedValue(value);
+  return decoded === undefined ? undefined : decodeSystemdSubstitutions(decoded, false);
+}
+
+function parseSystemdEscapedValue(value: string): string | undefined {
+  const quoted = value.startsWith('"') || value.endsWith('"');
+  if (quoted && (!value.startsWith('"') || !value.endsWith('"'))) return undefined;
+  return systemdUnescape(quoted ? value.slice(1, -1) : value);
+}
+
+function systemdUnescape(value: string): string | undefined {
   let result = "";
   for (let index = 0; index < value.length; index += 1) {
     const character = value[index];
-    if (character === "\\" && index + 1 < value.length) {
-      result += value[index + 1] ?? "";
-      index += 1;
-    } else {
+    if (character !== "\\") {
       result += character ?? "";
+      continue;
     }
+
+    const escape = value[index + 1];
+    if (escape === undefined) return undefined;
+    const simpleEscapes: Readonly<Record<string, string>> = {
+      "\\": "\\",
+      '"': '"',
+      "'": "'",
+      a: "\u0007",
+      b: "\b",
+      e: "\u001b",
+      f: "\f",
+      n: "\n",
+      r: "\r",
+      s: " ",
+      t: "\t",
+      v: "\v",
+    };
+    const simple = simpleEscapes[escape];
+    if (simple !== undefined) {
+      result += simple;
+      index += 1;
+      continue;
+    }
+
+    const length = escape === "x" ? 2 : escape === "u" ? 4 : escape === "U" ? 8 : 0;
+    if (length === 0) return undefined;
+    const encoded = value.slice(index + 2, index + 2 + length);
+    if (encoded.length !== length || !new RegExp(`^[0-9a-fA-F]{${String(length)}}$`, "u").test(encoded)) return undefined;
+    const codePoint = Number.parseInt(encoded, 16);
+    if (codePoint === 0 || codePoint > 0x10ffff) return undefined;
+    result += String.fromCodePoint(codePoint);
+    index += length + 1;
   }
   return result;
 }
 
-function parseShellQuotedValue(shell: NativeServiceShell["name"], value: string): string | undefined {
+function decodeSystemdSubstitutions(value: string, decodeDollars: boolean): string | undefined {
+  let result = "";
+  for (let index = 0; index < value.length; index += 1) {
+    const character = value[index];
+    if (character !== "%" && !(decodeDollars && character === "$")) {
+      result += character ?? "";
+      continue;
+    }
+    if (value[index + 1] !== character) return undefined;
+    result += character;
+    index += 1;
+  }
+  return result;
+}
+
+function parseSystemdShellCommand(shell: NativeServiceShell["name"], value: string): string | undefined {
+  if (value.startsWith('"') || value.endsWith('"')) return parseSystemdExecArgument(value);
   if (!value.startsWith("'") || !value.endsWith("'")) return undefined;
   const inner = value.slice(1, -1);
-  if (shell === "fish") return fishSingleQuoteUnescape(inner);
-  return inner.replaceAll("'\\''", "'").replaceAll("$$", "$").replaceAll("%%", "%");
+  const unquoted = shell === "fish" ? fishSingleQuoteUnescape(inner) : inner.replaceAll("'\\''", "'");
+  return decodeSystemdSubstitutions(unquoted, true);
 }
 
 function fishSingleQuoteUnescape(value: string): string {
@@ -395,16 +540,38 @@ function fishSingleQuoteUnescape(value: string): string {
       result += character ?? "";
     }
   }
-  return result.replaceAll("$$", "$").replaceAll("%%", "%");
+  return result;
 }
 
-function launchdString(contents: string, key: string): string | null {
-  const escapedKey = key.replaceAll(/[.*+?^${}()|[\]\\]/gu, "\\$&");
-  const value = new RegExp(`<key>${escapedKey}<\\/key>\\s*<string>([\\s\\S]*?)<\\/string>`, "u").exec(contents)?.[1];
-  return value === undefined ? null : xmlUnescape(value);
+function parseXmlStringSequence(contents: string): string[] | undefined {
+  const values: string[] = [];
+  let cursor = 0;
+  for (const match of contents.matchAll(/<string>([\s\S]*?)<\/string>/gu)) {
+    if (contents.slice(cursor, match.index).trim() !== "") return undefined;
+    const value = xmlUnescapeStrict(match[1] ?? "");
+    if (value === undefined) return undefined;
+    values.push(value);
+    cursor = match.index + match[0].length;
+  }
+  return contents.slice(cursor).trim() === "" ? values : undefined;
 }
 
-function xmlUnescape(value: string): string {
+function parseXmlStringDictionary(contents: string): Record<string, string> | undefined {
+  const values: Record<string, string> = {};
+  let cursor = 0;
+  for (const match of contents.matchAll(/<key>([\s\S]*?)<\/key>\s*<string>([\s\S]*?)<\/string>/gu)) {
+    if (contents.slice(cursor, match.index).trim() !== "") return undefined;
+    const key = xmlUnescapeStrict(match[1] ?? "");
+    const value = xmlUnescapeStrict(match[2] ?? "");
+    if (key === undefined || value === undefined || Object.hasOwn(values, key)) return undefined;
+    values[key] = value;
+    cursor = match.index + match[0].length;
+  }
+  return contents.slice(cursor).trim() === "" ? values : undefined;
+}
+
+function xmlUnescapeStrict(value: string): string | undefined {
+  if (/[<>]/u.test(value) || /&(?!(?:apos|quot|gt|lt|amp);)/u.test(value)) return undefined;
   return value
     .replaceAll("&apos;", "'")
     .replaceAll("&quot;", '"')

src/nativeServices/serviceInstall.test.ts

@@ -1,5 +1,8 @@
 import { describe, expect, it, vi } from "vitest";
-import { installNativeServiceCandidate } from "./serviceInstall.js";
+import {
+  installNativeServiceCandidate,
+  nativeServiceInstallFailureNeedsPathAdvice,
+} from "./serviceInstall.js";
 import type {
   NativeServiceAuthoritativeProbe,
   NativeServicePlan,
@@ -76,6 +79,41 @@ describe("native service install orchestration", () => {
     expect(replaceServices).toHaveBeenCalledWith(expect.objectContaining({ mode: "production" }));
   });
 
+  it("validates manager and shell readiness without executing configured overrides", async () => {
+    const writeInitialConfig = vi.fn<() => Promise<void>>(() => Promise.resolve());
+    const replaceServices = vi.fn<() => Promise<void>>(() => Promise.resolve());
+    const requests: NativeServiceProbeRequest[] = [];
+    const configuredInput: ProductionNativeServicePlanInput = {
+      ...productionInput,
+      executables: {
+        sessiond: { ...productionInput.executables.sessiond, configuredCommand: "custom-sessiond --flag" },
+        web: { ...productionInput.executables.web, configuredCommand: "custom-web --flag" },
+      },
+    };
+
+    const result = await installNativeServiceCandidate(
+      { mode: "production", input: configuredInput },
+      {
+        probe: {
+          run: (request) => {
+            requests.push(request);
+            return Promise.resolve({ kind: "infrastructure-failure", reason: "manager", message: "manager unavailable" });
+          },
+        },
+        fileExists: () => false,
+        writeInitialConfig,
+        replaceServices,
+      },
+    );
+
+    expect(result).toMatchObject({ ok: false, failure: { kind: "plan-validation" } });
+    if (result.ok) throw new Error("Expected manager validation failure");
+    expect(nativeServiceInstallFailureNeedsPathAdvice(result.failure)).toBe(false);
+    expect(requests).toEqual([expect.objectContaining({ purpose: "plan-validation", prerequisites: [] })]);
+    expect(writeInitialConfig).not.toHaveBeenCalled();
+    expect(replaceServices).not.toHaveBeenCalled();
+  });
+
   it("does not make durable changes when exact plan requirements are unsatisfied", async () => {
     const writeInitialConfig = vi.fn<() => Promise<void>>(() => Promise.resolve());
     const replaceServices = vi.fn<() => Promise<void>>(() => Promise.resolve());
@@ -99,6 +137,7 @@ describe("native service install orchestration", () => {
     if (result.ok || result.failure.kind !== "plan-validation") throw new Error("Expected validation failure");
     expect(result.failure.failures).not.toHaveLength(0);
     expect(result.failure.failures.every((failure) => failure.kind === "prerequisite-unsatisfied")).toBe(true);
+    expect(nativeServiceInstallFailureNeedsPathAdvice(result.failure)).toBe(true);
     expect(writeInitialConfig).not.toHaveBeenCalled();
     expect(replaceServices).not.toHaveBeenCalled();
   });
@@ -135,6 +174,8 @@ describe("native service install orchestration", () => {
         }],
       },
     });
+    if (result.ok) throw new Error("Expected infrastructure failure");
+    expect(nativeServiceInstallFailureNeedsPathAdvice(result.failure)).toBe(false);
     expect(writeInitialConfig).not.toHaveBeenCalled();
     expect(replaceServices).not.toHaveBeenCalled();
   });

src/nativeServices/serviceInstall.ts

@@ -1,5 +1,6 @@
 import {
   createDevelopmentNativeServicePlan,
+  nativeServicePrerequisiteNeedsPathAdvice,
   resolveProductionNativeServicePlan,
   validateNativeServicePlan,
   type DevelopmentNativeServicePlanInput,
@@ -29,6 +30,16 @@ export type NativeServiceInstallResult =
   | { ok: true; plan: NativeServicePlan }
   | { ok: false; failure: NativeServiceInstallFailure };
 
+export function nativeServiceInstallFailureNeedsPathAdvice(failure: NativeServiceInstallFailure): boolean {
+  if (failure.kind === "plan-resolution") {
+    return failure.failures.every((item) => item.kind === "executable-unavailable")
+      && failure.failures.length > 0;
+  }
+  return failure.failures.some((item) =>
+    item.kind === "prerequisite-unsatisfied"
+    && nativeServicePrerequisiteNeedsPathAdvice(item.prerequisite));
+}
+
 /**
  * Keeps preflight effects ahead of durable install effects. The authoritative
  * probes may create bounded temporary artifacts, but they must clean those up

src/nativeServices/servicePlan.test.ts

@@ -164,7 +164,14 @@ describe("production native service planning", () => {
         prerequisites: [],
       },
     ]);
-    expect(planValidationProbeRequests(resolution.plan)).toEqual([]);
+    expect(planValidationProbeRequests(resolution.plan)).toEqual([{
+      purpose: "plan-validation",
+      backend,
+      shell,
+      environment: { PI_WEB_CONFIG: "/home/user/.config/pi-web/config.json" },
+      workingDirectory: null,
+      prerequisites: [],
+    }]);
   });
 
   it("falls back per service to bundled entrypoints when named commands are unavailable", async () => {

src/nativeServices/servicePlan.ts

@@ -162,6 +162,7 @@ export interface DevelopmentNativeServicePlanInput {
 
 export interface NativeServicePlanDependencies {
   probe: NativeServiceAuthoritativeProbe;
+  /** Returns true only when the path exists and is a regular file. */
   fileExists(path: string): boolean;
 }
 
@@ -206,6 +207,10 @@ export type NativeServicePlanValidation =
   | { ok: true }
   | { ok: false; failures: readonly NativeServicePlanValidationFailure[] };
 
+export function nativeServicePrerequisiteNeedsPathAdvice(prerequisite: NativeServicePrerequisite): boolean {
+  return prerequisite.kind === "command-available" || prerequisite.kind === "node-version";
+}
+
 export const nativeServiceManagerRefs: Readonly<Record<NativeServiceId, NativeServiceManagerRef>> = {
   sessiond: {
     systemdName: "pi-web-sessiond.service",
@@ -386,7 +391,6 @@ export function createDevelopmentNativeServicePlan(input: DevelopmentNativeServi
 export function planValidationProbeRequests(plan: NativeServicePlan): readonly NativeServiceProbeRequest[] {
   const requests: (Omit<NativeServiceProbeRequest, "prerequisites"> & { prerequisites: NativeServicePrerequisite[] })[] = [];
   for (const service of plan.services) {
-    if (service.prerequisites.length === 0) continue;
     const existing = requests.find((request) =>
       request.workingDirectory === service.workingDirectory
       && environmentsEqual(request.environment, service.environment));
@@ -558,7 +562,7 @@ function commandRequirement(serviceId: NativeServiceId, command: string): Native
     id: commandRequirementId(serviceId, command),
     kind: "command-available",
     command,
-    description: `${command} is available to the service shell`,
+    description: `${command} resolves to an external executable for the service shell`,
   };
 }
 
@@ -577,7 +581,7 @@ function readableFileRequirement(serviceId: NativeServiceId, path: string): Nati
     id: `${serviceId}.entrypoint`,
     kind: "readable-file",
     path,
-    description: `bundled entrypoint is readable: ${path}`,
+    description: `bundled entrypoint is a readable regular file: ${path}`,
   };
 }
 

src/nativeServices/serviceProbe.test.ts

@@ -1,8 +1,10 @@
 import { describe, expect, it, vi } from "vitest";
 import {
   LaunchdNativeServiceProbe,
+  SpawnProbeCommandRunner,
   SystemdNativeServiceProbe,
   launchdProbePlist,
+  nativeServicePrerequisiteShellCheck,
   systemdRunArguments,
   type LaunchdProbeFileSystem,
   type ProbeCommandResult,
@@ -74,6 +76,8 @@ describe("systemd authoritative native-service probe", () => {
       "--pipe",
       "--quiet",
       "--unit=pi-web-authoritative-probe-fixed.service",
+      "--property=RuntimeMaxSec=15s",
+      "--property=TimeoutStopSec=5s",
       "--setenv=PI_WEB_CONFIG=/home/user/config with space.json",
       "--working-directory=/checkout with space",
       "/usr/bin/env",
@@ -91,7 +95,7 @@ describe("systemd authoritative native-service probe", () => {
       outcomes: [{
         prerequisiteId: "sessiond.command.npm",
         status: "unsatisfied",
-        detail: "npm was not found in the native service environment.",
+        detail: "npm did not resolve to an external executable in the native service environment.",
       }],
     });
 
@@ -106,7 +110,7 @@ describe("systemd authoritative native-service probe", () => {
     const runner = queuedRunner([
       { kind: "timeout", stdout: "", stderr: "" },
       completed(0),
-      completed(0),
+      completed(0, "not-found\n"),
     ]);
     const probe = new SystemdNativeServiceProbe({
       commandRunner: runner,
@@ -125,7 +129,7 @@ describe("systemd authoritative native-service probe", () => {
     const runner = queuedRunner([
       { kind: "timeout", stdout: "", stderr: "" },
       completed(0),
-      completed(1, "", "unit still loaded"),
+      completed(0, "loaded\n", "unit still loaded"),
     ]);
     const probe = new SystemdNativeServiceProbe({
       commandRunner: runner,
@@ -139,22 +143,43 @@ describe("systemd authoritative native-service probe", () => {
     expect(runner.calls.map(({ command, args }) => [command, ...args.slice(0, 3)])).toEqual([
       ["systemd-run", "--user", "--wait", "--collect"],
       ["systemctl", "--user", "stop", "pi-web-authoritative-probe-fixed.service"],
-      ["systemctl", "--user", "reset-failed", "pi-web-authoritative-probe-fixed.service"],
+      ["systemctl", "--user", "show", "pi-web-authoritative-probe-fixed.service"],
     ]);
   });
 });
 
+describe("spawn probe command runner", () => {
+  it("bounds captured command output", async () => {
+    const runner = new SpawnProbeCommandRunner();
+    const result = await runner.run(
+      process.execPath,
+      ["-e", "process.stdout.write('x'.repeat(2 * 1024 * 1024))"],
+      5_000,
+    );
+
+    expect(result).toMatchObject({ kind: "output-limit" });
+    expect(result.stdout.length).toBeLessThanOrEqual(1024 * 1024);
+  });
+
+  it("settles a timeout without waiting for inherited pipes to close", async () => {
+    const runner = new SpawnProbeCommandRunner();
+    const childScript = [
+      "const { spawn } = require('node:child_process');",
+      "const child = spawn(process.execPath, ['-e', 'setTimeout(() => {}, 1000)'], { stdio: ['ignore', 'inherit', 'inherit'] });",
+      "child.unref();",
+    ].join(" ");
+    const startedAt = performance.now();
+
+    await expect(runner.run(process.execPath, ["-e", childScript], 20)).resolves.toMatchObject({ kind: "timeout" });
+    expect(performance.now() - startedAt).toBeLessThan(500);
+  });
+});
+
 describe("launchd authoritative native-service probe", () => {
   it("bootstraps a uniquely labelled one-shot agent in gui/<uid> and always cleans it up", async () => {
-    const runner = queuedRunner([
-      completed(0),
-      completed(0, "state = running\n"),
-      completed(0, "state = not running\nlast exit code = 0\n"),
-      completed(0),
-    ]);
+    const runner = queuedRunner([completed(0), completed(0)]);
     const fileSystem = launchdFileSystem({
-      "/tmp/probe/stdout.log": marker("sessiond.command.npm", "satisfied"),
-      "/tmp/probe/stderr.log": "",
+      "/tmp/probe/result.log": marker("sessiond.command.npm", "satisfied"),
     });
     let now = 0;
     const probe = new LaunchdNativeServiceProbe({
@@ -172,28 +197,28 @@ describe("launchd authoritative native-service probe", () => {
     await expect(probe.run(request("launchd"))).resolves.toMatchObject({ kind: "completed" });
     expect(runner.calls.map(({ command, args }) => [command, ...args])).toEqual([
       ["launchctl", "bootstrap", "gui/501", "/tmp/probe/probe.plist"],
-      ["launchctl", "print", "gui/501/com.pi-web.authoritative-probe.501.fixed"],
-      ["launchctl", "print", "gui/501/com.pi-web.authoritative-probe.501.fixed"],
       ["launchctl", "bootout", "gui/501/com.pi-web.authoritative-probe.501.fixed"],
     ]);
     expect(fileSystem.writeFile).toHaveBeenCalledWith(
       "/tmp/probe/probe.plist",
       expect.stringContaining("<string>/bin/zsh</string>"),
+      0o600,
     );
     expect(fileSystem.writeFile).toHaveBeenCalledWith(
       "/tmp/probe/probe.plist",
       expect.stringContaining("<key>WorkingDirectory</key>\n  <string>/checkout with space</string>"),
+      0o600,
+    );
+    expect(fileSystem.writeFile).toHaveBeenCalledWith(
+      "/tmp/probe/probe.plist",
+      expect.stringContaining("/bin/mv &apos;/tmp/probe/result.pending&apos; &apos;/tmp/probe/result.log&apos;"),
+      0o600,
     );
     expect(fileSystem.removeDirectory).toHaveBeenCalledWith("/tmp/probe");
   });
 
   it("times out deterministically, boots out the agent, and removes temporary files", async () => {
-    const runner = queuedRunner([
-      completed(0),
-      completed(0, "state = running\n"),
-      completed(0, "state = running\n"),
-      completed(0),
-    ]);
+    const runner = queuedRunner([completed(0), completed(0)]);
     const fileSystem = launchdFileSystem({});
     let now = 0;
     const probe = new LaunchdNativeServiceProbe({
@@ -219,15 +244,34 @@ describe("launchd authoritative native-service probe", () => {
     expect(fileSystem.removeDirectory).toHaveBeenCalledWith("/tmp/probe");
   });
 
+  it("bounds a stalled result-file read before cleaning up", async () => {
+    const runner = queuedRunner([completed(0), completed(0)]);
+    const fileSystem = launchdFileSystem({});
+    fileSystem.readOptionalFile.mockReturnValueOnce(new Promise(() => undefined));
+    const probe = new LaunchdNativeServiceProbe({
+      commandRunner: runner,
+      fileSystem,
+      uid: 502,
+      createUniqueId: () => "fixed",
+      now: () => 0,
+      sleep: () => Promise.resolve(),
+      probeTimeoutMs: 10,
+      pollIntervalMs: 1,
+      commandTimeoutMs: 100,
+    });
+
+    await expect(probe.run(request("launchd"))).resolves.toMatchObject({
+      kind: "infrastructure-failure",
+      reason: "timeout",
+    });
+    expect(runner.calls.map(({ args }) => args[0])).toEqual(["bootstrap", "bootout"]);
+    expect(fileSystem.removeDirectory).toHaveBeenCalledWith("/tmp/probe");
+  });
+
   it("surfaces cleanup failure instead of returning an otherwise successful probe", async () => {
-    const runner = queuedRunner([
-      completed(0),
-      completed(0, "state = not running\nlast exit code = 0\n"),
-      completed(1, "", "bootout denied"),
-    ]);
+    const runner = queuedRunner([completed(0), completed(1, "", "bootout denied")]);
     const fileSystem = launchdFileSystem({
-      "/tmp/probe/stdout.log": marker("sessiond.command.npm", "satisfied"),
-      "/tmp/probe/stderr.log": "",
+      "/tmp/probe/result.log": marker("sessiond.command.npm", "satisfied"),
     });
     const probe = new LaunchdNativeServiceProbe({
       commandRunner: runner,
@@ -247,10 +291,9 @@ describe("launchd authoritative native-service probe", () => {
     expect(fileSystem.removeDirectory).toHaveBeenCalledWith("/tmp/probe");
   });
 
-  it("checks and boots out a label when bootstrap itself times out", async () => {
+  it("boots out a label when bootstrap itself times out", async () => {
     const runner = queuedRunner([
       { kind: "timeout", stdout: "", stderr: "" },
-      completed(0, "state = running\n"),
       completed(0),
     ]);
     const fileSystem = launchdFileSystem({});
@@ -270,12 +313,15 @@ describe("launchd authoritative native-service probe", () => {
       kind: "infrastructure-failure",
       reason: "timeout",
     });
-    expect(runner.calls.map(({ args }) => args[0])).toEqual(["bootstrap", "print", "bootout"]);
+    expect(runner.calls.map(({ args }) => args[0])).toEqual(["bootstrap", "bootout"]);
     expect(fileSystem.removeDirectory).toHaveBeenCalledWith("/tmp/probe");
   });
 
-  it("removes temporary files when bootstrap fails without booting out an unloaded label", async () => {
-    const runner = queuedRunner([completed(1, "", "bootstrap denied")]);
+  it("treats an explicit not-loaded bootout response as successful cleanup after bootstrap fails", async () => {
+    const runner = queuedRunner([
+      completed(1, "", "bootstrap denied"),
+      completed(3, "", "Could not find service in domain"),
+    ]);
     const fileSystem = launchdFileSystem({});
     const probe = new LaunchdNativeServiceProbe({
       commandRunner: runner,
@@ -292,17 +338,13 @@ describe("launchd authoritative native-service probe", () => {
     const result = await probe.run(request("launchd"));
     expect(result).toMatchObject({ kind: "infrastructure-failure", reason: "manager" });
     expect(result.kind === "infrastructure-failure" && result.message).toContain("bootstrap denied");
-    expect(runner.calls).toHaveLength(1);
+    expect(runner.calls.map(({ args }) => args[0])).toEqual(["bootstrap", "bootout"]);
     expect(fileSystem.removeDirectory).toHaveBeenCalledWith("/tmp/probe");
   });
 
-  it("cleans a loaded label after malformed launchctl output", async () => {
-    const runner = queuedRunner([
-      completed(0),
-      completed(0, "pid = 123\n"),
-      completed(0),
-    ]);
-    const fileSystem = launchdFileSystem({});
+  it("cleans a loaded label after malformed private result output", async () => {
+    const runner = queuedRunner([completed(0), completed(0)]);
+    const fileSystem = launchdFileSystem({ "/tmp/probe/result.log": "malformed result" });
     const probe = new LaunchdNativeServiceProbe({
       commandRunner: runner,
       fileSystem,
@@ -323,13 +365,10 @@ describe("launchd authoritative native-service probe", () => {
     expect(fileSystem.removeDirectory).toHaveBeenCalledWith("/tmp/probe");
   });
 
-  it("cleans a loaded label when probe output cannot be read", async () => {
-    const runner = queuedRunner([
-      completed(0),
-      completed(0, "state = not running\nlast exit code = 0\n"),
-      completed(0),
-    ]);
+  it("cleans a loaded label when the private result cannot be read", async () => {
+    const runner = queuedRunner([completed(0), completed(0)]);
     const fileSystem = launchdFileSystem({});
+    fileSystem.readOptionalFile.mockRejectedValueOnce(new Error("read denied"));
     const probe = new LaunchdNativeServiceProbe({
       commandRunner: runner,
       fileSystem,
@@ -344,13 +383,16 @@ describe("launchd authoritative native-service probe", () => {
 
     const result = await probe.run(request("launchd"));
     expect(result).toMatchObject({ kind: "infrastructure-failure", reason: "manager" });
-    expect(result.kind === "infrastructure-failure" && result.message).toContain("Could not read launchd probe output");
+    expect(result.kind === "infrastructure-failure" && result.message).toContain("Could not read launchd probe result");
     expect(runner.calls.at(-1)?.args[0]).toBe("bootout");
     expect(fileSystem.removeDirectory).toHaveBeenCalledWith("/tmp/probe");
   });
 
   it("reports temporary-file cleanup failures", async () => {
-    const runner = queuedRunner([completed(1, "", "bootstrap denied")]);
+    const runner = queuedRunner([
+      completed(1, "", "bootstrap denied"),
+      completed(3, "", "Could not find service in domain"),
+    ]);
     const fileSystem = launchdFileSystem({});
     fileSystem.removeDirectory.mockRejectedValueOnce(new Error("rm denied"));
     const probe = new LaunchdNativeServiceProbe({
@@ -372,28 +414,70 @@ describe("launchd authoritative native-service probe", () => {
 });
 
 describe("probe service definitions", () => {
+  it("requires external executables instead of accepting shell functions or aliases", () => {
+    const commandRequirement = request().prerequisites[0];
+    if (commandRequirement === undefined) throw new Error("Expected a command prerequisite");
+    const bashCheck = nativeServicePrerequisiteShellCheck("bash", commandRequirement);
+    expect(bashCheck).toContain("case \"$pi_web_probe_executable\" in */*)");
+    expect(bashCheck).toContain("test -f \"$pi_web_probe_executable\"");
+    expect(bashCheck).toContain("test -x \"$pi_web_probe_executable\"");
+
+    const fishCheck = nativeServicePrerequisiteShellCheck("fish", commandRequirement);
+    expect(fishCheck).toContain("string match -q '*/*'");
+    expect(fishCheck).toContain("test -f $pi_web_probe_executable[1]");
+    expect(fishCheck).toContain("test -x $pi_web_probe_executable[1]");
+  });
+
+  it("invokes the resolved external Node executable for version checks", () => {
+    const check = nativeServicePrerequisiteShellCheck("zsh", {
+      id: "sessiond.node",
+      kind: "node-version",
+      command: "node",
+      minimumMajor: 22,
+      description: "node >= 22",
+    });
+    expect(check).toContain("\"$pi_web_probe_executable\" '-e'");
+    expect(check).not.toContain("&& node -e");
+  });
+
+  it("requires bundled entrypoints to be readable regular files", () => {
+    const check = nativeServicePrerequisiteShellCheck("bash", {
+      id: "sessiond.entrypoint",
+      kind: "readable-file",
+      path: "/package/server.js",
+      description: "entrypoint",
+    });
+    expect(check).toBe("test -f '/package/server.js' && test -r '/package/server.js'");
+  });
+
   it("renders backend inputs without inheriting the caller PATH", () => {
     const probeRequest = request();
-    expect(systemdRunArguments(probeRequest, "probe.service", "echo ok")).not.toContain(expect.stringContaining("PATH="));
+    const systemdArguments = systemdRunArguments(probeRequest, "probe.service", "echo ok");
+    expect(systemdArguments.some((argument) => argument.includes("PATH="))).toBe(false);
     const plist = launchdProbePlist(probeRequest, "com.example.probe", "echo ok", "/tmp/out", "/tmp/err");
     expect(plist).not.toContain("<key>PATH</key>");
     expect(plist).toContain("<key>PI_WEB_CONFIG</key>");
+    expect(plist).toContain("<key>HardResourceLimits</key>");
+  });
+
+  it("escapes manager-side substitutions in the systemd probe payload", () => {
+    const args = systemdRunArguments(request(), "probe.service", "test -r '/tmp/$HOME/%h'");
+    expect(args.at(-1)).toBe("test -r '/tmp/$$HOME/%h'");
   });
 });
 
 function launchdFileSystem(contents: Record<string, string>): LaunchdProbeFileSystem & {
   writeFile: ReturnType<typeof vi.fn<LaunchdProbeFileSystem["writeFile"]>>;
+  readOptionalFile: ReturnType<typeof vi.fn<LaunchdProbeFileSystem["readOptionalFile"]>>;
   removeDirectory: ReturnType<typeof vi.fn<LaunchdProbeFileSystem["removeDirectory"]>>;
 } {
   const writeFileMock = vi.fn<LaunchdProbeFileSystem["writeFile"]>(() => Promise.resolve());
+  const readOptionalFileMock = vi.fn<LaunchdProbeFileSystem["readOptionalFile"]>((path) => Promise.resolve(contents[path] ?? null));
   const removeDirectoryMock = vi.fn<LaunchdProbeFileSystem["removeDirectory"]>(() => Promise.resolve());
   return {
     createTemporaryDirectory: () => Promise.resolve("/tmp/probe"),
     writeFile: writeFileMock,
-    readFile: (path) => {
-      const content = contents[path];
-      return content === undefined ? Promise.reject(new Error(`missing ${path}`)) : Promise.resolve(content);
-    },
+    readOptionalFile: readOptionalFileMock,
     removeDirectory: removeDirectoryMock,
   };
 }

src/nativeServices/serviceProbe.ts

@@ -2,6 +2,7 @@ import { spawn } from "node:child_process";
 import { mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
 import { tmpdir, userInfo } from "node:os";
 import { join } from "node:path";
+import { performance } from "node:perf_hooks";
 import { randomUUID } from "node:crypto";
 import type {
   NativeServiceAuthoritativeProbe,
@@ -15,7 +16,8 @@ import type {
 export type ProbeCommandResult =
   | { kind: "completed"; status: number; stdout: string; stderr: string }
   | { kind: "timeout"; stdout: string; stderr: string }
-  | { kind: "spawn-failure"; message: string; stdout: string; stderr: string };
+  | { kind: "spawn-failure"; message: string; stdout: string; stderr: string }
+  | { kind: "output-limit"; stdout: string; stderr: string };
 
 export interface ProbeCommandRunner {
   run(command: string, args: readonly string[], timeoutMs: number): Promise<ProbeCommandResult>;
@@ -23,8 +25,8 @@ export interface ProbeCommandRunner {
 
 export interface LaunchdProbeFileSystem {
   createTemporaryDirectory(prefix: string): Promise<string>;
-  writeFile(path: string, contents: string): Promise<void>;
-  readFile(path: string): Promise<string>;
+  writeFile(path: string, contents: string, mode: number): Promise<void>;
+  readOptionalFile(path: string): Promise<string | null>;
   removeDirectory(path: string): Promise<void>;
 }
 
@@ -48,6 +50,8 @@ export interface LaunchdProbeDependencies extends CommonProbeDependencies {
 const defaultCommandTimeoutMs = 15_000;
 const defaultProbeTimeoutMs = 15_000;
 const defaultPollIntervalMs = 50;
+const maxCapturedCommandOutputBytes = 1024 * 1024;
+const maxLaunchdProbeFileBytes = 1024 * 1024;
 
 export class SystemdNativeServiceProbe implements NativeServiceAuthoritativeProbe {
   public constructor(private readonly dependencies: SystemdProbeDependencies) {}
@@ -64,12 +68,12 @@ export class SystemdNativeServiceProbe implements NativeServiceAuthoritativeProb
     const args = systemdRunArguments(request, unitName, command);
     const result = await this.dependencies.commandRunner.run("systemd-run", args, this.dependencies.commandTimeoutMs);
 
-    if (result.kind === "timeout") {
+    if (result.kind === "timeout" || result.kind === "output-limit") {
       const cleanupFailure = await this.cleanupTimedOutUnit(unitName);
-      return cleanupFailure ?? infrastructureFailure(
-        "timeout",
-        `Timed out waiting for transient systemd unit ${unitName}.`,
-      );
+      if (cleanupFailure !== null) return cleanupFailure;
+      return result.kind === "timeout"
+        ? infrastructureFailure("timeout", `Timed out waiting for transient systemd unit ${unitName}.`)
+        : infrastructureFailure("manager", `Transient systemd probe ${unitName} exceeded the output limit.`);
     }
     if (result.kind === "spawn-failure") {
       return infrastructureFailure("manager", `Could not start systemd-run: ${result.message}`);
@@ -89,18 +93,19 @@ export class SystemdNativeServiceProbe implements NativeServiceAuthoritativeProb
       ["--user", "stop", unitName],
       this.dependencies.commandTimeoutMs,
     );
-    if (stop.kind !== "completed" || stop.status !== 0) {
-      return infrastructureFailure("cleanup", `Could not stop timed-out transient systemd unit ${unitName}: ${commandFailureDetail(stop)}`);
-    }
-    const reset = await this.dependencies.commandRunner.run(
+    const inspected = await this.dependencies.commandRunner.run(
       "systemctl",
-      ["--user", "reset-failed", unitName],
+      ["--user", "show", unitName, "--property=LoadState", "--value"],
       this.dependencies.commandTimeoutMs,
     );
-    if (reset.kind !== "completed" || reset.status !== 0) {
-      return infrastructureFailure("cleanup", `Could not collect timed-out transient systemd unit ${unitName}: ${commandFailureDetail(reset)}`);
+    if (inspected.kind === "completed" && inspected.status === 0 && inspected.stdout.trim() === "not-found") {
+      return null;
     }
-    return null;
+    const details = [
+      `stop: ${commandFailureDetail(stop)}`,
+      `load state: ${commandFailureDetail(inspected)}`,
+    ].join("; ");
+    return infrastructureFailure("cleanup", `Could not confirm cleanup of timed-out transient systemd unit ${unitName}: ${details}`);
   }
 }
 
@@ -128,10 +133,18 @@ export class LaunchdNativeServiceProbe implements NativeServiceAuthoritativeProb
       const plistPath = join(directory, "probe.plist");
       const stdoutPath = join(directory, "stdout.log");
       const stderrPath = join(directory, "stderr.log");
-      const command = prerequisiteProbeCommand(request.shell.name, request.prerequisites, outputPrefix);
+      const pendingResultPath = join(directory, "result.pending");
+      const resultPath = join(directory, "result.log");
+      const command = prerequisiteProbeCommand(
+        request.shell.name,
+        request.prerequisites,
+        outputPrefix,
+        { pendingPath: pendingResultPath, completedPath: resultPath },
+      );
       await this.dependencies.fileSystem.writeFile(
         plistPath,
         launchdProbePlist(request, label, command, stdoutPath, stderrPath),
+        0o600,
       );
 
       const bootstrap = await this.dependencies.commandRunner.run(
@@ -140,11 +153,11 @@ export class LaunchdNativeServiceProbe implements NativeServiceAuthoritativeProb
         this.dependencies.commandTimeoutMs,
       );
       if (bootstrap.kind !== "completed" || bootstrap.status !== 0) {
-        bootstrapState = bootstrap.kind === "timeout" ? "uncertain" : "not-loaded";
+        bootstrapState = bootstrap.kind === "spawn-failure" ? "not-loaded" : "uncertain";
         result = commandInfrastructureFailure("bootstrap launchd probe", bootstrap);
       } else {
         bootstrapState = "loaded";
-        result = await this.waitForResult(target, stdoutPath, stderrPath, request.prerequisites, outputPrefix);
+        result = await this.waitForResult(target, resultPath, request.prerequisites, outputPrefix);
       }
     } catch (error: unknown) {
       result = infrastructureFailure("manager", `Could not prepare launchd probe: ${errorMessage(error)}`);
@@ -156,48 +169,25 @@ export class LaunchdNativeServiceProbe implements NativeServiceAuthoritativeProb
 
   private async waitForResult(
     target: string,
-    stdoutPath: string,
-    stderrPath: string,
+    resultPath: string,
     prerequisites: readonly NativeServicePrerequisite[],
     outputPrefix: string,
   ): Promise<NativeServiceProbeResult> {
     const deadline = this.dependencies.now() + this.dependencies.probeTimeoutMs;
     while (this.dependencies.now() < deadline) {
-      const printed = await this.dependencies.commandRunner.run(
-        "launchctl",
-        ["print", target],
-        this.dependencies.commandTimeoutMs,
+      const remainingMs = Math.max(0, deadline - this.dependencies.now());
+      const boundedRead = await readOptionalFileBounded(
+        this.dependencies.fileSystem,
+        resultPath,
+        remainingMs,
       );
-      if (printed.kind !== "completed" || printed.status !== 0) {
-        return commandInfrastructureFailure("inspect launchd probe", printed);
+      if (boundedRead.kind === "deadline") break;
+      if (boundedRead.kind === "read-failure") {
+        return infrastructureFailure("manager", `Could not read launchd probe result: ${errorMessage(boundedRead.error)}`);
       }
-
-      const state = launchdField(printed.stdout, "state");
-      if (state === undefined) {
-        return infrastructureFailure("malformed-output", `launchctl returned no state for ${target}.`);
-      }
-      const lastExitCode = launchdIntegerField(printed.stdout, "last exit code");
-      if (state === "not running" && lastExitCode !== undefined) {
-        let stdout: string;
-        let stderr: string;
-        try {
-          [stdout, stderr] = await Promise.all([
-            this.dependencies.fileSystem.readFile(stdoutPath),
-            this.dependencies.fileSystem.readFile(stderrPath),
-          ]);
-        } catch (error: unknown) {
-          return infrastructureFailure("manager", `Could not read launchd probe output: ${errorMessage(error)}`);
-        }
-        if (lastExitCode !== 0) {
-          return infrastructureFailure(
-            "manager",
-            `Launchd probe service exited with status ${String(lastExitCode)}: ${firstOutput(stderr, stdout, "no output")}`,
-          );
-        }
-        return parseProbeOutput(stdout, prerequisites, outputPrefix);
-      }
-
-      await this.dependencies.sleep(this.dependencies.pollIntervalMs);
+      if (boundedRead.output !== null) return parseProbeOutput(boundedRead.output, prerequisites, outputPrefix);
+      const pollDelayMs = Math.min(this.dependencies.pollIntervalMs, Math.max(0, deadline - this.dependencies.now()));
+      await this.dependencies.sleep(pollDelayMs);
     }
     return infrastructureFailure("timeout", `Timed out waiting for launchd probe ${target}.`);
   }
@@ -208,28 +198,21 @@ export class LaunchdNativeServiceProbe implements NativeServiceAuthoritativeProb
     bootstrapState: "not-loaded" | "loaded" | "uncertain",
   ): Promise<NativeServiceProbeResult | null> {
     const failures: string[] = [];
-    let shouldBootout = bootstrapState === "loaded";
-    if (bootstrapState === "uncertain") {
-      const inspection = await this.dependencies.commandRunner.run(
-        "launchctl",
-        ["print", target],
-        this.dependencies.commandTimeoutMs,
-      );
-      if (inspection.kind === "completed") {
-        shouldBootout = inspection.status === 0;
-      } else {
-        // If launchctl cannot tell us whether a timed-out bootstrap loaded the
-        // label, bootout is the only operation that can make cleanup certain.
-        shouldBootout = true;
-      }
-    }
+    const shouldBootout = bootstrapState !== "not-loaded";
     if (shouldBootout) {
+      // A failed or timed-out bootstrap may still have loaded the unique label.
+      // Bootout is the only race-free cleanup; an explicit not-loaded response
+      // is success when bootstrap completion was uncertain.
+      const absenceIsSuccess = bootstrapState === "uncertain";
       const bootout = await this.dependencies.commandRunner.run(
         "launchctl",
         ["bootout", target],
         this.dependencies.commandTimeoutMs,
       );
-      if (bootout.kind !== "completed" || bootout.status !== 0) {
+      if (
+        (bootout.kind !== "completed" || bootout.status !== 0)
+        && !(absenceIsSuccess && launchdTargetNotLoaded(bootout))
+      ) {
         failures.push(`bootout failed: ${commandFailureDetail(bootout)}`);
       }
     }
@@ -258,7 +241,7 @@ export function createNativeServiceAuthoritativeProbe(): NativeServiceAuthoritat
     ...common,
     fileSystem: nodeLaunchdProbeFileSystem,
     uid: userInfo().uid,
-    now: Date.now,
+    now: performance.now.bind(performance),
     sleep: (milliseconds) => new Promise((resolve) => setTimeout(resolve, milliseconds)),
     probeTimeoutMs: defaultProbeTimeoutMs,
     pollIntervalMs: defaultPollIntervalMs,
@@ -280,15 +263,21 @@ export function systemdRunArguments(
     "--pipe",
     "--quiet",
     `--unit=${unitName}`,
+    "--property=RuntimeMaxSec=15s",
+    "--property=TimeoutStopSec=5s",
     ...Object.entries(request.environment).map(([key, value]) => `--setenv=${key}=${value}`),
     ...(request.workingDirectory === null ? [] : [`--working-directory=${request.workingDirectory}`]),
     "/usr/bin/env",
-    request.shell.executable,
+    escapeSystemdCommandExpansion(request.shell.executable),
     "-lc",
-    shellCommand,
+    escapeSystemdCommandExpansion(shellCommand),
   ];
 }
 
+function escapeSystemdCommandExpansion(value: string): string {
+  return value.replaceAll("$", () => "$$");
+}
+
 export function launchdProbePlist(
   request: NativeServiceProbeRequest,
   label: string,
@@ -316,36 +305,63 @@ ${argumentsXml}
   </array>
 ${workingDirectoryXml}${environmentXml}  <key>RunAtLoad</key>
   <true/>
+  <key>HardResourceLimits</key>
+  <dict>
+    <key>FileSize</key>
+    <integer>${String(maxLaunchdProbeFileBytes)}</integer>
+  </dict>
 ${plistString("StandardOutPath", stdoutPath)}${plistString("StandardErrorPath", stderrPath)}</dict>
 </plist>
 `;
 }
 
-class SpawnProbeCommandRunner implements ProbeCommandRunner {
+export class SpawnProbeCommandRunner implements ProbeCommandRunner {
   public run(command: string, args: readonly string[], timeoutMs: number): Promise<ProbeCommandResult> {
     return new Promise((resolve) => {
       const child = spawn(command, args, { stdio: ["ignore", "pipe", "pipe"] });
       let stdout = "";
       let stderr = "";
+      let capturedBytes = 0;
       let spawnFailure: string | null = null;
-      let timedOut = false;
+      let settled = false;
+
+      const finish = (result: ProbeCommandResult, terminate: boolean): void => {
+        if (settled) return;
+        settled = true;
+        clearTimeout(timeout);
+        if (terminate) {
+          child.kill("SIGKILL");
+          child.stdout.destroy();
+          child.stderr.destroy();
+          child.unref();
+        }
+        resolve(result);
+      };
+      const capture = (stream: "stdout" | "stderr", chunk: string): void => {
+        if (settled) return;
+        const bytes = Buffer.byteLength(chunk);
+        if (capturedBytes + bytes > maxCapturedCommandOutputBytes) {
+          finish({ kind: "output-limit", stdout, stderr }, true);
+          return;
+        }
+        capturedBytes += bytes;
+        if (stream === "stdout") stdout += chunk;
+        else stderr += chunk;
+      };
+
       child.stdout.setEncoding("utf8");
       child.stderr.setEncoding("utf8");
-      child.stdout.on("data", (chunk: string) => { stdout += chunk; });
-      child.stderr.on("data", (chunk: string) => { stderr += chunk; });
+      child.stdout.on("data", (chunk: string) => { capture("stdout", chunk); });
+      child.stderr.on("data", (chunk: string) => { capture("stderr", chunk); });
       child.on("error", (error) => { spawnFailure = error.message; });
       const timeout = setTimeout(() => {
-        timedOut = true;
-        child.kill("SIGKILL");
+        finish({ kind: "timeout", stdout, stderr }, true);
       }, timeoutMs);
       child.on("close", (status) => {
-        clearTimeout(timeout);
-        if (timedOut) {
-          resolve({ kind: "timeout", stdout, stderr });
-        } else if (spawnFailure !== null) {
-          resolve({ kind: "spawn-failure", message: spawnFailure, stdout, stderr });
+        if (spawnFailure !== null) {
+          finish({ kind: "spawn-failure", message: spawnFailure, stdout, stderr }, false);
         } else {
-          resolve({ kind: "completed", status: status ?? 1, stdout, stderr });
+          finish({ kind: "completed", status: status ?? 1, stdout, stderr }, false);
         }
       });
     });
@@ -354,49 +370,109 @@ class SpawnProbeCommandRunner implements ProbeCommandRunner {
 
 const nodeLaunchdProbeFileSystem: LaunchdProbeFileSystem = {
   createTemporaryDirectory: (prefix) => mkdtemp(prefix),
-  writeFile: (path, contents) => writeFile(path, contents, "utf8"),
-  readFile: (path) => readFile(path, "utf8"),
+  writeFile: (path, contents, mode) => writeFile(path, contents, { encoding: "utf8", mode }),
+  readOptionalFile: async (path) => {
+    try {
+      return await readFile(path, "utf8");
+    } catch (error: unknown) {
+      if (isNodeErrorWithCode(error, "ENOENT")) return null;
+      throw error;
+    }
+  },
   removeDirectory: (path) => rm(path, { recursive: true, force: true }),
 };
 
+function readOptionalFileBounded(
+  fileSystem: LaunchdProbeFileSystem,
+  path: string,
+  timeoutMs: number,
+): Promise<
+  | { kind: "read"; output: string | null }
+  | { kind: "read-failure"; error: unknown }
+  | { kind: "deadline" }
+> {
+  return new Promise((resolve) => {
+    let settled = false;
+    const finish = (result:
+      | { kind: "read"; output: string | null }
+      | { kind: "read-failure"; error: unknown }
+      | { kind: "deadline" }): void => {
+      if (settled) return;
+      settled = true;
+      clearTimeout(timeout);
+      resolve(result);
+    };
+    const timeout = setTimeout(() => { finish({ kind: "deadline" }); }, timeoutMs);
+    void fileSystem.readOptionalFile(path).then(
+      (output) => { finish({ kind: "read", output }); },
+      (error: unknown) => { finish({ kind: "read-failure", error }); },
+    );
+  });
+}
+
 function prerequisiteProbeCommand(
   shell: NativeServiceShellName,
   prerequisites: readonly NativeServicePrerequisite[],
   outputPrefix: string,
+  resultFiles?: { pendingPath: string; completedPath: string },
 ): string {
-  return prerequisites.map((prerequisite) => {
+  const markerPath = resultFiles?.pendingPath;
+  const checks = prerequisites.map((prerequisite) => {
     const check = nativeServicePrerequisiteShellCheck(shell, prerequisite);
     const encodedId = Buffer.from(prerequisite.id, "utf8").toString("base64");
-    const satisfied = markerCommand(shell, outputPrefix, encodedId, "satisfied");
-    const unsatisfied = markerCommand(shell, outputPrefix, encodedId, "unsatisfied");
+    const satisfied = markerCommand(shell, outputPrefix, encodedId, "satisfied", markerPath);
+    const unsatisfied = markerCommand(shell, outputPrefix, encodedId, "unsatisfied", markerPath);
     return `${check} >/dev/null 2>&1 && ${satisfied} || ${unsatisfied}`;
   }).join("; ") || ":";
+  if (resultFiles === undefined) return checks;
+  const pending = shellQuote(shell, resultFiles.pendingPath);
+  const completed = shellQuote(shell, resultFiles.completedPath);
+  return `printf '%s' '' > ${pending}; ${checks}; /bin/mv ${pending} ${completed}`;
 }
 
 export function nativeServicePrerequisiteShellCheck(shell: NativeServiceShellName, prerequisite: NativeServicePrerequisite): string {
   switch (prerequisite.kind) {
     case "command-available":
-      return `command -v ${shellQuote(shell, prerequisite.command)}`;
+      return externalExecutableShellCheck(shell, prerequisite.command);
     case "node-version": {
       const script = `const major=Number(process.versions.node.split('.')[0]);process.exit(major>=${String(prerequisite.minimumMajor)}?0:1)`;
-      return `node -e ${shellQuote(shell, script)}`;
+      return externalExecutableShellCheck(shell, "node", ["-e", script]);
+    }
+    case "readable-file": {
+      const path = shellQuote(shell, prerequisite.path);
+      return `test -f ${path} && test -r ${path}`;
     }
-    case "readable-file":
-      return `test -r ${shellQuote(shell, prerequisite.path)}`;
     case "package-scripts": {
       const script = "const p=require(process.argv[1]);const names=process.argv.slice(2);process.exit(names.every((name)=>typeof p.scripts?.[name]==='string')?0:1)";
-      return ["node", "-e", shellQuote(shell, script), shellQuote(shell, prerequisite.packageJsonPath), ...prerequisite.scripts.map((name) => shellQuote(shell, name))].join(" ");
+      return externalExecutableShellCheck(shell, "node", ["-e", script, prerequisite.packageJsonPath, ...prerequisite.scripts]);
     }
   }
 }
 
+function externalExecutableShellCheck(
+  shell: NativeServiceShellName,
+  command: string,
+  arguments_: readonly string[] = [],
+): string {
+  const quotedCommand = shellQuote(shell, command);
+  const quotedArguments = arguments_.map((argument) => shellQuote(shell, argument)).join(" ");
+  if (shell === "fish") {
+    const invocation = quotedArguments === "" ? "" : `; and $pi_web_probe_executable[1] ${quotedArguments}`;
+    return `set -l pi_web_probe_executable (command -v ${quotedCommand}); and test (count $pi_web_probe_executable) -eq 1; and string match -q '*/*' -- $pi_web_probe_executable[1]; and test -f $pi_web_probe_executable[1]; and test -x $pi_web_probe_executable[1]${invocation}`;
+  }
+  const invocation = quotedArguments === "" ? "" : ` && "$pi_web_probe_executable" ${quotedArguments}`;
+  return `pi_web_probe_executable=$(command -v ${quotedCommand}) && case "$pi_web_probe_executable" in */*) test -f "$pi_web_probe_executable" && test -x "$pi_web_probe_executable"${invocation};; *) false;; esac`;
+}
+
 function markerCommand(
   shell: NativeServiceShellName,
   outputPrefix: string,
   encodedId: string,
   status: "satisfied" | "unsatisfied",
+  outputPath?: string,
 ): string {
-  return `printf '%s\\t%s\\t%s\\n' ${shellQuote(shell, outputPrefix)} ${shellQuote(shell, encodedId)} ${shellQuote(shell, status)}`;
+  const redirect = outputPath === undefined ? "" : ` >> ${shellQuote(shell, outputPath)}`;
+  return `printf '%s\\t%s\\t%s\\n' ${shellQuote(shell, outputPrefix)} ${shellQuote(shell, encodedId)} ${shellQuote(shell, status)}${redirect}`;
 }
 
 function parseProbeOutput(
@@ -440,11 +516,11 @@ function parseProbeOutput(
 function unsatisfiedDetail(prerequisite: NativeServicePrerequisite): string {
   switch (prerequisite.kind) {
     case "command-available":
-      return `${prerequisite.command} was not found in the native service environment.`;
+      return `${prerequisite.command} did not resolve to an external executable in the native service environment.`;
     case "node-version":
       return `node >= ${String(prerequisite.minimumMajor)} was not available in the native service environment.`;
     case "readable-file":
-      return `${prerequisite.path} was not readable in the native service environment.`;
+      return `${prerequisite.path} was not a readable regular file in the native service environment.`;
     case "package-scripts":
       return `${prerequisite.packageJsonPath} did not provide scripts ${prerequisite.scripts.join(", ")} in the native service environment.`;
   }
@@ -461,18 +537,9 @@ function safeUniqueId(value: string): string {
   return safe === "" ? "probe" : safe;
 }
 
-function launchdField(output: string, field: string): string | undefined {
-  return new RegExp(`^\\s*${escapeRegExp(field)}\\s*=\\s*(.+)$`, "mu").exec(output)?.[1]?.trim();
-}
-
-function launchdIntegerField(output: string, field: string): number | undefined {
-  const value = launchdField(output, field);
-  if (value === undefined || !/^-?\d+$/u.test(value)) return undefined;
-  return Number(value);
-}
-
-function escapeRegExp(value: string): string {
-  return value.replaceAll(/[.*+?^${}()|[\]\\]/gu, "\\$&");
+function launchdTargetNotLoaded(result: ProbeCommandResult): boolean {
+  if (result.kind !== "completed" || result.status === 0) return false;
+  return /(?:could not find (?:specified )?service|service not found|no such process)/iu.test(`${result.stderr}\n${result.stdout}`);
 }
 
 function plistString(key: string, value: string, indent = "  "): string {
@@ -496,6 +563,7 @@ function commandInfrastructureFailure(action: string, result: ProbeCommandResult
 function commandFailureDetail(result: ProbeCommandResult): string {
   if (result.kind === "timeout") return "command timed out";
   if (result.kind === "spawn-failure") return result.message;
+  if (result.kind === "output-limit") return "command output exceeded the capture limit";
   return firstOutput(result.stderr, result.stdout, `exit status ${String(result.status)}`);
 }
 
@@ -517,3 +585,7 @@ function firstOutput(...values: string[]): string {
 function errorMessage(error: unknown): string {
   return error instanceof Error ? error.message : String(error);
 }
+
+function isNodeErrorWithCode(error: unknown, code: string): error is NodeJS.ErrnoException {
+  return error instanceof Error && "code" in error && error.code === code;
+}

src/nativeServices/serviceRendering.test.ts

@@ -34,12 +34,33 @@ describe("native service rendering", () => {
 
     expect(unit).toContain("Description=PI WEB UI dev server");
     expect(unit).toContain("After=pi-web-sessiond.service\nWants=pi-web-sessiond.service");
-    expect(unit).toContain('WorkingDirectory="/checkout with space"');
+    expect(unit).toContain("WorkingDirectory=/checkout\\x20with\\x20space");
     expect(unit).toContain('Environment="PI_WEB_CONFIG=/home/user/config with \\"quote\\".json"');
-    expect(unit).toContain("ExecStart=/usr/bin/env /bin/zsh -lc 'exec /usr/bin/env bash -c '\\''trap");
+    expect(unit).toContain('ExecStart=/usr/bin/env "/bin/zsh" -lc "exec /usr/bin/env bash -c \'trap \\"kill 0\\" EXIT;');
     expect(unit).toContain("Restart=no");
   });
 
+  it("escapes systemd specifiers and line controls without changing directives", () => {
+    const plan = createDevelopmentNativeServicePlan({
+      backend: { kind: "systemd", label: "systemd" },
+      shell: {
+        name: "bash",
+        executable: "/shell $HOME/%h/bash",
+        source: "detected",
+        detectedExecutable: "/shell $HOME/%h/bash",
+      },
+      environment: { PI_WEB_CONFIG: "/config/%h\nEnvironment=INJECTED=yes" },
+      workingDirectory: "/checkout %h\nwith newline",
+      packageJsonPath: "/checkout/package.json",
+    });
+    const unit = renderSystemdUnit(plan, planService(plan, 0));
+
+    expect(unit).toContain("WorkingDirectory=/checkout\\x20%%h\\nwith\\x20newline");
+    expect(unit).toContain('Environment="PI_WEB_CONFIG=/config/%%h\\nEnvironment=INJECTED=yes"');
+    expect(unit).toContain('ExecStart=/usr/bin/env "/shell $$HOME/%%h/bash"');
+    expect(unit.match(/^Environment=/gmu)).toHaveLength(1);
+  });
+
   it("renders launchd entirely from the canonical plan", () => {
     const plan = developmentPlan("launchd");
     const plist = renderLaunchdPlist(plan, planService(plan, 0), "/logs");

src/nativeServices/serviceRendering.ts

@@ -3,7 +3,6 @@ import type {
   NativeServiceId,
   NativeServicePlan,
   NativeServicePlanService,
-  NativeServiceShellName,
 } from "./servicePlan.js";
 
 export function renderSystemdUnit(
@@ -14,7 +13,7 @@ export function renderSystemdUnit(
   assertBackend(plan, "systemd");
   const workingDirectory = service.workingDirectory === null
     ? ""
-    : `WorkingDirectory=${systemdQuotedValue(service.workingDirectory)}\n`;
+    : `WorkingDirectory=${systemdPathValue(service.workingDirectory)}\n`;
   const restart = service.restart === "on-failure"
     ? "Restart=on-failure\nRestartSec=2\n"
     : "Restart=no\n";
@@ -22,7 +21,7 @@ export function renderSystemdUnit(
 Description=${service.description}
 ${systemdDependencyLine(plan, "After", service.after)}${systemdDependencyLine(plan, "Wants", service.wants)}[Service]
 Type=simple
-${workingDirectory}${systemdEnvironmentLines(service.environment)}ExecStart=/usr/bin/env ${plan.shell.executable} -lc ${systemdServiceShellQuote(plan.shell.name, service.shellCommand)}
+${workingDirectory}${systemdEnvironmentLines(service.environment)}ExecStart=/usr/bin/env ${systemdExecArgument(plan.shell.executable)} -lc ${systemdExecArgument(service.shellCommand)}
 ${restart}
 [Install]
 WantedBy=default.target
@@ -83,20 +82,37 @@ function systemdDependencyLine(
 
 function systemdEnvironmentLines(environment: Readonly<Record<string, string>>): string {
   return Object.entries(environment)
-    .map(([key, value]) => `Environment="${systemdEscape(key)}=${systemdEscape(value)}"\n`)
+    .map(([key, value]) => `Environment=${systemdQuotedDirectiveValue(`${key}=${value}`)}\n`)
     .join("");
 }
 
-function systemdServiceShellQuote(shell: NativeServiceShellName, value: string): string {
-  return shellQuote(shell, value.replaceAll("%", "%%").replaceAll("$", "$$"));
+function systemdExecArgument(value: string): string {
+  return `"${systemdEscape(value.replaceAll("%", "%%").replaceAll("$", () => "$$"), false)}"`;
 }
 
-function systemdQuotedValue(value: string): string {
-  return `"${systemdEscape(value)}"`;
+function systemdQuotedDirectiveValue(value: string): string {
+  return `"${systemdEscape(value.replaceAll("%", "%%"), false)}"`;
 }
 
-function systemdEscape(value: string): string {
-  return value.replaceAll("\\", "\\\\").replaceAll('"', '\\"');
+function systemdPathValue(value: string): string {
+  return systemdEscape(value.replaceAll("%", "%%"), true);
+}
+
+function systemdEscape(value: string, escapeSpaces: boolean): string {
+  let escaped = "";
+  for (const character of value) {
+    const code = character.codePointAt(0) ?? 0;
+    if (character === "\\") escaped += "\\\\";
+    else if (character === '"') escaped += escapeSpaces ? "\\x22" : '\\"';
+    else if (character === "'" && escapeSpaces) escaped += "\\x27";
+    else if (character === " " && escapeSpaces) escaped += "\\x20";
+    else if (character === "\n") escaped += "\\n";
+    else if (character === "\r") escaped += "\\r";
+    else if (character === "\t") escaped += "\\t";
+    else if (code < 0x20 || code === 0x7f) escaped += `\\x${code.toString(16).padStart(2, "0")}`;
+    else escaped += character;
+  }
+  return escaped;
 }
 
 function plistProgramArguments(arguments_: readonly string[]): string {
@@ -113,12 +129,6 @@ function plistString(key: string, value: string, indent = "  "): string {
   return `${indent}<key>${xmlEscape(key)}</key>\n${indent}<string>${xmlEscape(value)}</string>\n`;
 }
 
-function shellQuote(shell: NativeServiceShellName, value: string): string {
-  return shell === "fish"
-    ? `'${value.replaceAll("\\", "\\\\").replaceAll("'", "\\'")}'`
-    : `'${value.replaceAll("'", "'\\''")}'`;
-}
-
 function xmlEscape(value: string): string {
   return value
     .replaceAll("&", "&amp;")