fix(sessions): clarify subsession join guidance

.changeset/clarify-subsession-waiting.md

@@ -2,4 +2,4 @@
 "@jmfederico/pi-web": patch
 ---
 
-Keep delegation tools available to human-created and independently spawned sessions, remove them from tracked child sessions, and make delegation tool contracts capability-focused.
+Keep delegation tools available to human-created and independently spawned sessions, remove them from tracked child sessions, and guide parent agents to track required subsessions and yield at a join point instead of polling.

docs/config.html

@@ -513,8 +513,19 @@
                 to be enabled.
               </p>
               <p>
-                Tracked subsessions let an agent delegate work to child sessions, get notified when children stop
-                working, and inspect their transcripts. Restart the session daemon after changing this setting.
+                Tracked subsessions let an agent delegate work to child sessions, receive a notification when each child
+                stops working, and inspect their status and transcripts. Calling <code>spawn_subsession</code> returns
+                immediately. The parent can continue independent work while treating every child whose result it needs
+                as pending. Before producing work that depends on those results, the parent reaches a join point and
+                yields until every required child has sent a completion notice.
+              </p>
+              <p>
+                A completion notice wakes an idle parent. If the parent is busy, the notice queues until the current
+                turn ends rather than interrupting in-flight work. For multiple required children, each notice resolves
+                one pending child; after processing it, the parent yields again if another required child is pending.
+                <code>list_subsessions</code>, <code>check_subsession</code>, and <code>read_subsession</code> provide
+                on-demand status and transcript inspection for deliberate progress checks or recovery. Completion
+                notifications, rather than polling these tools, are the normal synchronization mechanism.
               </p>
               <p>
                 In <strong>Settings → Session daemon</strong>, these keys are saved on the selected machine. Restart the

docs/config.md

@@ -171,7 +171,9 @@ The per-request size limit is still controlled by `maxUploadBytes` / `PI_WEB_MAX
 
 `subsessions` is beta and controls whether agents receive the tracked-subsession tools: `spawn_subsession`, `list_subsessions`, `check_subsession`, and `read_subsession`. It defaults to `false` and also requires `spawnSessions` to be enabled.
 
-Tracked subsessions let an agent delegate work to child sessions, get notified when children stop working, and inspect their transcripts.
+Tracked subsessions let an agent delegate work to child sessions, receive a notification when each child stops working, and inspect their status and transcripts. Calling `spawn_subsession` returns immediately. The parent can continue independent work while treating every child whose result it needs as pending. Before producing work that depends on those results, the parent reaches a join point and yields until every required child has sent a completion notice.
+
+A completion notice wakes an idle parent. If the parent is busy, the notice queues until the current turn ends rather than interrupting in-flight work. For multiple required children, each notice resolves one pending child; after processing it, the parent yields again if another required child is pending. `list_subsessions`, `check_subsession`, and `read_subsession` provide on-demand status and transcript inspection for deliberate progress checks or recovery. Completion notifications, rather than polling these tools, are the normal synchronization mechanism.
 
 In **Settings → Session daemon**, these keys are saved on the selected machine. Restart the session daemon on that machine after changing them.
 

src/server/sessions/spawnSubsessionTool.test.ts

@@ -52,26 +52,25 @@ describe("createSubsessionToolDefinitions", () => {
     expect(firstText(result.content)).toContain("Started tracked subsession child-1");
   });
 
-  it("describes tracked dispatch and notification without workflow policy", async () => {
+  it("guides the parent to join all required subsessions without polling", async () => {
     const { spawn: spawnTool } = tools({
       spawn: vi.fn(() => Promise.resolve({ sessionId: "child-1", cwd: "/repos/a-feature" })),
     });
 
-    expect(spawnTool.description).toBe("Start a tracked child session and send it an initial prompt. The call returns after dispatch; the parent is notified when the child stops working and can inspect its status, latest output, and transcript.");
+    expect(spawnTool.description).toBe("Start a tracked child and return after dispatch. Track required children as pending: continue independent work, then yield at a join point until all have notified completion. Notifications queue while the parent is busy; do not poll for completion.");
+    expect(spawnTool.promptSnippet).toBe("spawn_subsession: delegate parallel work; yield at a join point until all required children complete.");
 
     const result = await spawnTool.execute("call-contract", { prompt: "do it" }, undefined, undefined, ctxFor("parent-1", undefined));
-    const message = firstText(result.content);
-    expect(message).toBe("Started tracked subsession child-1 in /repos/a-feature. The parent will be notified when it stops working.");
-    expect(`${spawnTool.description}\n${message}`).not.toMatch(/do not poll|continue (?:useful|independent) work|end (?:this|the) turn|relay/i);
+    expect(firstText(result.content)).toBe("Started tracked subsession child-1 in /repos/a-feature. Track it as pending and, before finalizing dependent work, yield until all required children have notified completion.");
   });
 
-  it("keeps all subsession tool descriptions capability-oriented", () => {
+  it("keeps subsession inspection tool descriptions capability-oriented", () => {
     const definitions = tools({});
 
     expect(definitions.list.description).toBe("List tracked child sessions owned by the calling session, with each child's current status (working, idle, error, or unknown).");
     expect(definitions.check.description).toBe("Return a tracked subsession's current status, message count, and most recent assistant output.");
     expect(definitions.read.description).toBe("Return a filtered, paginated transcript of a tracked subsession. Filters select message roles and content kinds, search full message content, optionally include raw tool arguments, and cap or page the returned entries.");
-    for (const definition of Object.values(definitions)) {
+    for (const definition of [definitions.list, definitions.check, definitions.read]) {
       expect(definition.description).not.toMatch(/use this|do not poll|continue working|start narrow|for just the final|relay/i);
     }
   });

src/server/sessions/spawnSubsessionTool.ts

@@ -178,8 +178,8 @@ export function createSubsessionToolDefinitions(spawningCwd: string, deps: Subse
   const spawnTool = defineTool<typeof SpawnSubsessionParams, SpawnSubsessionResult>({
     name: "spawn_subsession",
     label: "Spawn subsession",
-    description: "Start a tracked child session and send it an initial prompt. The call returns after dispatch; the parent is notified when the child stops working and can inspect its status, latest output, and transcript.",
-    promptSnippet: "spawn_subsession: start a tracked child session you will be notified about",
+    description: "Start a tracked child and return after dispatch. Track required children as pending: continue independent work, then yield at a join point until all have notified completion. Notifications queue while the parent is busy; do not poll for completion.",
+    promptSnippet: "spawn_subsession: delegate parallel work; yield at a join point until all required children complete.",
     parameters: SpawnSubsessionParams,
     async execute(_toolCallId, params, _signal, _onUpdate, ctx) {
       const parentSessionId = ctx.sessionManager.getSessionId();
@@ -193,7 +193,7 @@ export function createSubsessionToolDefinitions(spawningCwd: string, deps: Subse
         ...(ctx.model === undefined ? {} : { model: ctx.model }),
       });
       return {
-        content: [{ type: "text", text: `Started tracked subsession ${result.sessionId} in ${result.cwd}. The parent will be notified when it stops working.` }],
+        content: [{ type: "text", text: `Started tracked subsession ${result.sessionId} in ${result.cwd}. Track it as pending and, before finalizing dependent work, yield until all required children have notified completion.` }],
         details: result,
       };
     },