diff --git a/.ai-work/01-fix-lint-and-ci.md b/.ai-work/01-fix-lint-and-ci.md
index 553f542..0a22573 100644
--- a/.ai-work/01-fix-lint-and-ci.md
+++ b/.ai-work/01-fix-lint-and-ci.md
@@ -1,6 +1,6 @@
 # 01. Fix lint and add CI scripts
 
-Status: pending
+Status: completed
 
 Make the hygiene baseline green and easy to run locally/CI:
 
diff --git a/package.json b/package.json
index 4bb0ef1..eaa8ddf 100644
--- a/package.json
+++ b/package.json
@@ -12,6 +12,7 @@
     "build": "tsc && vite build",
     "typecheck": "tsc --noEmit",
     "lint": "eslint \"src/**/*.ts\" vite.config.ts",
+    "verify": "npm run typecheck && npm run lint",
     "start": "tsx src/server/index.ts",
     "start:sessiond": "tsx src/server/sessiond.ts"
   },
diff --git a/src/client/src/api.ts b/src/client/src/api.ts
index eb13dda..77e5e44 100644
--- a/src/client/src/api.ts
+++ b/src/client/src/api.ts
@@ -356,7 +356,9 @@ function parseFileTreeEntry(value: unknown): FileTreeEntry {
 
 function parseFileContentResponse(value: unknown): FileContentResponse {
   const record = requireRecord(value);
-  return { path: requireString(record, "path"), ...optionalField("language", optionalString(record, "language")), encoding: requireString(record, "encoding") as "utf8", size: requireNumber(record, "size"), modifiedAt: requireString(record, "modifiedAt"), content: requireString(record, "content"), truncated: requireBoolean(record, "truncated"), binary: requireBoolean(record, "binary") };
+  const encoding = requireString(record, "encoding");
+  if (encoding !== "utf8") throw new Error("Invalid file encoding");
+  return { path: requireString(record, "path"), ...optionalField("language", optionalString(record, "language")), encoding, size: requireNumber(record, "size"), modifiedAt: requireString(record, "modifiedAt"), content: requireString(record, "content"), truncated: requireBoolean(record, "truncated"), binary: requireBoolean(record, "binary") };
 }
 
 function parseGitStatusResponse(value: unknown): GitStatusResponse {
@@ -370,9 +372,20 @@ function parseGitStatusFile(value: unknown): GitStatusFile {
 }
 
 function parseGitFileState(value: unknown): GitFileState {
-  if (typeof value !== "string") throw new Error("Expected git file state");
-  if (!["unmodified", "modified", "added", "deleted", "renamed", "copied", "untracked", "ignored", "conflicted"].includes(value)) throw new Error("Invalid git file state");
-  return value as GitFileState;
+  switch (value) {
+    case "unmodified":
+    case "modified":
+    case "added":
+    case "deleted":
+    case "renamed":
+    case "copied":
+    case "untracked":
+    case "ignored":
+    case "conflicted":
+      return value;
+    default:
+      throw new Error("Invalid git file state");
+  }
 }
 
 function parseGitDiffResponse(value: unknown): GitDiffResponse {
diff --git a/src/client/src/chatHistoryCache.ts b/src/client/src/chatHistoryCache.ts
index 6868fe3..78bd196 100644
--- a/src/client/src/chatHistoryCache.ts
+++ b/src/client/src/chatHistoryCache.ts
@@ -36,7 +36,7 @@ export function writeChatHistoryCache(sessionId: string, page: RawMessagePage):
 }
 
 export function mergeChatHistory(existing: RawMessagePage | undefined, incoming: RawMessagePage): RawMessagePage {
-  if (!existing || existing.total !== incoming.total) return incoming;
+  if (existing?.total !== incoming.total) return incoming;
 
   const start = Math.min(existing.start, incoming.start);
   const end = Math.max(existing.start + existing.messages.length, incoming.start + incoming.messages.length);
diff --git a/src/client/src/chatMessages.ts b/src/client/src/chatMessages.ts
index 990a500..88e86f9 100644
--- a/src/client/src/chatMessages.ts
+++ b/src/client/src/chatMessages.ts
@@ -26,7 +26,7 @@ export function normalizeMessage(message: unknown): ChatLine[] {
   const parts = normalizeContent(getProperty(message, "content"), message);
   const skillLines = role === "user" ? normalizeSkillInvocation(parts) : undefined;
   if (skillLines !== undefined) return skillLines;
-  const source = normalizeSource(message, parts);
+  const source = normalizeSource(message);
   if (role === "tool") return [{ role, parts, ...(source === undefined ? {} : { source }) }];
 
   const visible = parts.filter((part) => part.type !== "empty");
@@ -44,7 +44,7 @@ function normalizeSkillInvocation(parts: ChatPart[]): ChatLine[] | undefined {
 }
 
 function parseSkillBlock(text: string): { name: string; location: string; content: string; userMessage?: string } | undefined {
-  const match = text.match(/^<skill name="([^"]+)" location="([^"]+)">\n([\s\S]*?)\n<\/skill>(?:\n\n([\s\S]+))?$/);
+  const match = /^<skill name="([^"]+)" location="([^"]+)">\n([\s\S]*?)\n<\/skill>(?:\n\n([\s\S]+))?$/.exec(text);
   if (match === null) return undefined;
   const userMessage = match[4]?.trim();
   return {
@@ -55,7 +55,7 @@ function parseSkillBlock(text: string): { name: string; location: string; conten
   };
 }
 
-function normalizeSource(message: unknown, _parts: ChatPart[]): ChatLine["source"] | undefined {
+function normalizeSource(message: unknown): ChatLine["source"] | undefined {
   const source = getString(message, "source");
   if (source === "compaction" || source === "branch_summary") return source;
   return undefined;
diff --git a/src/client/src/components/ChatView.ts b/src/client/src/components/ChatView.ts
index edd56b8..6e41ecf 100644
--- a/src/client/src/components/ChatView.ts
+++ b/src/client/src/components/ChatView.ts
@@ -86,11 +86,11 @@ export class ChatView extends LitElement {
     const olderCount = this.messageStart;
     const fullHistory = olderCount <= 0
       ? "full history loaded"
-      : `${olderCount} older not loaded · ${loadedPercent}% loaded`;
+      : `${String(olderCount)} older not loaded · ${String(loadedPercent)}% loaded`;
     return html`
       <div class="history-indicator">
         <div>${fullHistory}</div>
-        <div>loaded scroll: ${this.loadedScrollPercent}% from top</div>
+        <div>loaded scroll: ${String(this.loadedScrollPercent)}% from top</div>
       </div>
     `;
   }
diff --git a/src/client/src/components/CodeViewer.ts b/src/client/src/components/CodeViewer.ts
index 8d9e133..97280a4 100644
--- a/src/client/src/components/CodeViewer.ts
+++ b/src/client/src/components/CodeViewer.ts
@@ -97,6 +97,7 @@ const viewerTheme = EditorView.theme({
 });
 
 function languageExtensions(language: string | undefined): Extension[] {
+  if (language === undefined) return [];
   switch (language) {
     case "typescript": return [javascript({ typescript: true })];
     case "javascript": return [javascript()];
diff --git a/src/client/src/components/PiWebApp.ts b/src/client/src/components/PiWebApp.ts
index 83bb635..c1cbd46 100644
--- a/src/client/src/components/PiWebApp.ts
+++ b/src/client/src/components/PiWebApp.ts
@@ -149,9 +149,7 @@ export class PiWebApp extends LitElement {
     const workspace = this.state.selectedWorkspace;
     if (!project || !workspace) return;
     if (this.state.expandedDirs[path] !== undefined) {
-      const next = { ...this.state.expandedDirs };
-      delete next[path];
-      this.setState({ expandedDirs: next });
+      this.setState({ expandedDirs: omitKey(this.state.expandedDirs, path) });
       return;
     }
     try {
@@ -231,7 +229,7 @@ export class PiWebApp extends LitElement {
   }
 
   private renderWorkspacePanel() {
-    return html`<workspace-panel .workspace=${this.state.selectedWorkspace} .tool=${this.state.workspaceTool} .fileTree=${this.state.fileTree} .expandedDirs=${this.state.expandedDirs} .selectedFilePath=${this.state.selectedFilePath} .selectedFileContent=${this.state.selectedFileContent} .fileTreeStale=${this.state.fileTreeStale} .gitStatus=${this.state.gitStatus} .selectedDiffPath=${this.state.selectedDiffPath} .selectedDiff=${this.state.selectedDiff} .gitStale=${this.state.gitStale} .onSelectTool=${(tool: "files" | "git") => this.selectWorkspaceTool(tool)} .onRefreshFiles=${() => this.refreshFiles()} .onExpandDir=${(path: string) => this.expandDir(path)} .onSelectFile=${(path: string) => this.selectFile(path)} .onRefreshGit=${() => this.refreshGit()} .onSelectDiff=${(path: string) => this.selectDiff(path)}></workspace-panel>`;
+    return html`<workspace-panel .workspace=${this.state.selectedWorkspace} .tool=${this.state.workspaceTool} .fileTree=${this.state.fileTree} .expandedDirs=${this.state.expandedDirs} .selectedFilePath=${this.state.selectedFilePath} .selectedFileContent=${this.state.selectedFileContent} .fileTreeStale=${this.state.fileTreeStale} .gitStatus=${this.state.gitStatus} .selectedDiffPath=${this.state.selectedDiffPath} .selectedDiff=${this.state.selectedDiff} .gitStale=${this.state.gitStale} .onSelectTool=${(tool: "files" | "git") => { this.selectWorkspaceTool(tool); }} .onRefreshFiles=${() => this.refreshFiles()} .onExpandDir=${(path: string) => this.expandDir(path)} .onSelectFile=${(path: string) => this.selectFile(path)} .onRefreshGit=${() => this.refreshGit()} .onSelectDiff=${(path: string) => this.selectDiff(path)}></workspace-panel>`;
   }
 
   override render() {
@@ -249,9 +247,9 @@ export class PiWebApp extends LitElement {
         </aside>
         <main class=${`${state.mainView}-view`}>
           <div class="mobile-tabs">
-            <button class=${state.mainView === "chat" ? "selected" : ""} @click=${() => this.selectMainView("chat")}>Chat</button>
-            <button class=${state.mainView === "files" ? "selected" : ""} @click=${() => this.selectMainView("files")}>Files</button>
-            <button class=${state.mainView === "git" ? "selected" : ""} @click=${() => this.selectMainView("git")}>Git</button>
+            <button class=${state.mainView === "chat" ? "selected" : ""} @click=${() => { this.selectMainView("chat"); }}>Chat</button>
+            <button class=${state.mainView === "files" ? "selected" : ""} @click=${() => { this.selectMainView("files"); }}>Files</button>
+            <button class=${state.mainView === "git" ? "selected" : ""} @click=${() => { this.selectMainView("git"); }}>Git</button>
           </div>
           ${state.error ? html`<div class="error">${state.error}</div>` : null}
           ${state.selectedSession ? html`
@@ -274,6 +272,10 @@ function isActive(status: AppState["status"]): boolean {
   return status?.isStreaming === true || status?.isBashRunning === true || status?.isCompacting === true;
 }
 
+function omitKey<T>(record: Record<string, T>, keyToOmit: string): Record<string, T> {
+  return Object.fromEntries(Object.entries(record).filter(([key]) => key !== keyToOmit));
+}
+
 function nextFrame(): Promise<void> {
   return new Promise((resolve) => requestAnimationFrame(() => { resolve(); }));
 }
diff --git a/src/client/src/components/PromptEditor.ts b/src/client/src/components/PromptEditor.ts
index 86dbd13..69502b5 100644
--- a/src/client/src/components/PromptEditor.ts
+++ b/src/client/src/components/PromptEditor.ts
@@ -208,7 +208,7 @@ export class PromptEditor extends LitElement {
 function fileInsertText(path: string, pathMode: boolean, quoted: boolean): string {
   const prefix = pathMode ? "" : "@";
   if (!quoted && !path.includes(" ")) return `${prefix}${path}`;
-  return `${prefix}\"${path}\"`;
+  return `${prefix}"${path}"`;
 }
 
 function emptySlashCommands(): SlashCommand[] {
diff --git a/src/client/src/components/WorkspacePanel.ts b/src/client/src/components/WorkspacePanel.ts
index 3d9f6e3..5336e92 100644
--- a/src/client/src/components/WorkspacePanel.ts
+++ b/src/client/src/components/WorkspacePanel.ts
@@ -29,8 +29,8 @@ export class WorkspacePanel extends LitElement {
     return html`
       <header>
         <div class="tabs">
-          <button class=${this.tool === "files" ? "selected" : ""} @click=${() => this.onSelectTool("files")}>Files</button>
-          <button class=${this.tool === "git" ? "selected" : ""} @click=${() => this.onSelectTool("git")}>Git</button>
+          <button class=${this.tool === "files" ? "selected" : ""} @click=${() => { this.onSelectTool("files"); }}>Files</button>
+          <button class=${this.tool === "git" ? "selected" : ""} @click=${() => { this.onSelectTool("git"); }}>Git</button>
         </div>
         <small title=${this.workspace.path}>${this.workspace.label}</small>
       </header>
@@ -58,19 +58,25 @@ export class WorkspacePanel extends LitElement {
 
   private renderTreeEntry(entry: FileTreeEntry, depth: number): TemplateResult {
     const children = this.expandedDirs[entry.path];
+    const hasChildren = children !== undefined;
     return html`
-      <button class="row" style=${`--depth:${depth}`} @click=${() => entry.type === "directory" ? this.onExpandDir(entry.path) : this.onSelectFile(entry.path)}>
-        <span>${entry.type === "directory" ? (children ? "▾" : "▸") : "·"}</span>
+      <button class="row" style=${`--depth:${String(depth)}`} @click=${() => { this.selectTreeEntry(entry); }}>
+        <span>${entry.type === "directory" ? (hasChildren ? "▾" : "▸") : "·"}</span>
         <span>${entry.name}</span>
       </button>
-      ${children ? children.map((child) => this.renderTreeEntry(child, depth + 1)) : null}
+      ${hasChildren ? children.map((child) => this.renderTreeEntry(child, depth + 1)) : null}
     `;
   }
 
+  private selectTreeEntry(entry: FileTreeEntry): void {
+    if (entry.type === "directory") this.onExpandDir(entry.path);
+    else this.onSelectFile(entry.path);
+  }
+
   private renderFileViewer() {
     const file = this.selectedFileContent;
-    if (!this.selectedFilePath) return html`<p class="muted">Select a file.</p>`;
-    if (!file) return html`<p class="muted">Loading ${this.selectedFilePath}…</p>`;
+    if (this.selectedFilePath === undefined || this.selectedFilePath === "") return html`<p class="muted">Select a file.</p>`;
+    if (file === undefined) return html`<p class="muted">Loading ${this.selectedFilePath}…</p>`;
     if (file.binary) return html`<p class="muted">Binary file: ${file.path}</p>`;
     return html`
       <div class="viewer-header"><strong>${file.path}</strong><small>${file.language ?? "text"}${file.truncated ? " · truncated" : ""}</small></div>
@@ -88,10 +94,10 @@ export class WorkspacePanel extends LitElement {
       </section>
       <section class="split">
         <div class="list">
-          ${status === undefined ? html`<p class="muted">No status loaded.</p>` : status.isGitRepo === false ? html`<p class="muted">Not a git repository.</p>` : html`
-            <p class="summary">${status.branch ?? "detached"}${status.ahead || status.behind ? ` · ↑${status.ahead ?? 0} ↓${status.behind ?? 0}` : ""}</p>
+          ${status === undefined ? html`<p class="muted">No status loaded.</p>` : !status.isGitRepo ? html`<p class="muted">Not a git repository.</p>` : html`
+            <p class="summary">${this.gitSummary(status)}</p>
             ${status.files.length === 0 ? html`<p class="muted">No changes.</p>` : status.files.map((file) => html`
-              <button class="row ${this.selectedDiffPath === file.path ? "selected" : ""}" @click=${() => this.onSelectDiff(file.path)}>
+              <button class="row ${this.selectedDiffPath === file.path ? "selected" : ""}" @click=${() => { this.onSelectDiff(file.path); }}>
                 <span>${stateLabel(file.index, file.workingTree)}</span>
                 <span>${file.path}</span>
               </button>
@@ -106,15 +112,22 @@ export class WorkspacePanel extends LitElement {
   }
 
   private renderDiffViewer() {
-    if (!this.selectedDiffPath) return html`<p class="muted">Select a changed file.</p>`;
+    if (this.selectedDiffPath === undefined || this.selectedDiffPath === "") return html`<p class="muted">Select a changed file.</p>`;
     const diff = this.selectedDiff;
-    if (!diff) return html`<p class="muted">Loading diff…</p>`;
+    if (diff === undefined) return html`<p class="muted">Loading diff…</p>`;
     return html`
       <div class="viewer-header"><strong>${diff.path ?? "diff"}</strong><small>${diff.staged ? "staged" : "unstaged"}${diff.truncated ? " · truncated" : ""}</small></div>
-      <code-viewer .content=${diff.diff || "No unstaged diff."}></code-viewer>
+      <code-viewer .content=${diff.diff !== "" ? diff.diff : "No unstaged diff."}></code-viewer>
     `;
   }
 
+  private gitSummary(status: GitStatusResponse): string {
+    const branch = status.branch ?? "detached";
+    const ahead = status.ahead ?? 0;
+    const behind = status.behind ?? 0;
+    return ahead === 0 && behind === 0 ? branch : `${branch} · ↑${String(ahead)} ↓${String(behind)}`;
+  }
+
   static override styles = workspacePanelStyles;
 }
 
diff --git a/src/server/git/gitService.ts b/src/server/git/gitService.ts
index 61bcbb1..734c119 100644
--- a/src/server/git/gitService.ts
+++ b/src/server/git/gitService.ts
@@ -88,6 +88,7 @@ function parseStatus(raw: string): GitStatusResponse {
 }
 
 function stateFor(code: string | undefined): GitFileState {
+  if (code === undefined) return "unmodified";
   switch (code) {
     case ".": return "unmodified";
     case "M": return "modified";
diff --git a/src/server/workspaces/fileContentService.ts b/src/server/workspaces/fileContentService.ts
index 4208c47..983c696 100644
--- a/src/server/workspaces/fileContentService.ts
+++ b/src/server/workspaces/fileContentService.ts
@@ -41,7 +41,7 @@ function isProbablyBinary(buffer: Buffer): boolean {
 
 function languageForPath(path: string): { language?: string } {
   const ext = path.split(".").pop()?.toLowerCase();
-  const language = ext === undefined ? undefined : ({
+  const languages: Record<string, string | undefined> = {
     ts: "typescript",
     tsx: "typescript",
     js: "javascript",
@@ -56,6 +56,7 @@ function languageForPath(path: string): { language?: string } {
     sh: "shell",
     yml: "yaml",
     yaml: "yaml",
-  } as Record<string, string | undefined>)[ext];
+  };
+  const language = ext === undefined ? undefined : languages[ext];
   return language === undefined ? {} : { language };
 }