feat(KB-003): add task steering feature with UI and prompt injection

- Add SteeringComment type to core types for user steering input
- Add addSteeringComment method to TaskStore with persistence
- Add POST /api/tasks/:id/steer endpoint for adding steering comments
- Add frontend API client and SteeringTab UI component
- Inject steering comments into execution prompt for agent guidance
- Add comprehensive tests for store, API, UI, and executor components
- Include changeset for patch release

packages/engine/src/executor.test.ts

@@ -994,6 +994,83 @@ describe("buildExecutionPrompt", () => {
     expect(result).not.toContain("## Project Commands");
   });
 
+  it("includes Steering Comments section when steeringComments has entries", () => {
+    const task = createMockTaskDetail({
+      steeringComments: [
+        {
+          id: "1",
+          text: "Please handle the edge case",
+          createdAt: new Date().toISOString(),
+          author: "user" as const,
+        },
+      ],
+    });
+    const result = buildExecutionPrompt(task);
+
+    expect(result).toContain("## Steering Comments");
+    expect(result).toContain("**user**");
+    expect(result).toContain("> Please handle the edge case");
+    expect(result).toContain("The following steering comments were added by the user");
+  });
+
+  it("formats multiple steering comments correctly", () => {
+    const now = new Date();
+    const task = createMockTaskDetail({
+      steeringComments: [
+        {
+          id: "1",
+          text: "First comment",
+          createdAt: new Date(now.getTime() - 60000).toISOString(), // 1 minute ago
+          author: "user" as const,
+        },
+        {
+          id: "2",
+          text: "Second comment",
+          createdAt: now.toISOString(),
+          author: "agent" as const,
+        },
+      ],
+    });
+    const result = buildExecutionPrompt(task);
+
+    expect(result).toContain("**user**");
+    expect(result).toContain("**agent**");
+    expect(result).toContain("> First comment");
+    expect(result).toContain("> Second comment");
+  });
+
+  it("omits Steering Comments section when steeringComments is empty", () => {
+    const task = createMockTaskDetail({ steeringComments: [] });
+    const result = buildExecutionPrompt(task);
+
+    expect(result).not.toContain("## Steering Comments");
+  });
+
+  it("omits Steering Comments section when steeringComments is undefined", () => {
+    const task = createMockTaskDetail();
+    const result = buildExecutionPrompt(task);
+
+    expect(result).not.toContain("## Steering Comments");
+  });
+
+  it("includes only the 10 most recent steering comments", () => {
+    const steeringComments = Array.from({ length: 15 }, (_, i) => ({
+      id: `${i}`,
+      text: `Comment ${i}`,
+      createdAt: new Date().toISOString(),
+      author: "user" as const,
+    }));
+
+    const task = createMockTaskDetail({ steeringComments });
+    const result = buildExecutionPrompt(task);
+
+    // Should include comments 5-14 (the 10 most recent), not 0-4
+    expect(result).toContain("> Comment 5");
+    expect(result).toContain("> Comment 14");
+    expect(result).not.toContain("> Comment 0");
+    expect(result).not.toContain("> Comment 4");
+  });
+
   it("passes settings to buildExecutionPrompt in TaskExecutor.execute()", async () => {
     const store = createMockStore();
     store.getSettings.mockResolvedValue({

packages/engine/src/executor.ts

@@ -959,6 +959,25 @@ export class TaskExecutor {
   }
 }
 
+/**
+ * Format a timestamp for display in steering comments.
+ * Returns relative time for recent comments, absolute date for older ones.
+ */
+function formatTimestamp(iso: string): string {
+  const date = new Date(iso);
+  const now = new Date();
+  const diffMs = now.getTime() - date.getTime();
+  const diffMin = Math.floor(diffMs / 60000);
+  const diffHr = Math.floor(diffMin / 60);
+  const diffDay = Math.floor(diffHr / 24);
+
+  if (diffMin < 1) return "just now";
+  if (diffMin < 60) return `${diffMin}m ago`;
+  if (diffHr < 24) return `${diffHr}h ago`;
+  if (diffDay < 7) return `${diffDay}d ago`;
+  return date.toLocaleDateString();
+}
+
 // Project commands are injected here (for reliability) and also in the PROMPT.md (by triage).
 // This ensures the executor agent always sees the authoritative commands from settings,
 // even if the PROMPT.md was written manually or before commands were configured.
@@ -1019,6 +1038,26 @@ git log --oneline
     commandsSection = "\n" + lines.join("\n") + "\n";
   }
 
+  // Build steering comments section (last 10 comments only to avoid context bloat)
+  let steeringSection = "";
+  if (task.steeringComments && task.steeringComments.length > 0) {
+    const recentComments = [...task.steeringComments].slice(-10);
+    const lines = [
+      "",
+      "## Steering Comments",
+      "",
+      "The following steering comments were added by the user during execution. Consider adjusting your approach or replanning remaining steps based on this feedback.",
+      "",
+    ];
+    for (const comment of recentComments) {
+      const timestamp = formatTimestamp(comment.createdAt);
+      lines.push(`**${comment.author}** — ${timestamp}`);
+      lines.push(`> ${comment.text}`);
+      lines.push("");
+    }
+    steeringSection = lines.join("\n");
+  }
+
   return `Execute this task.
 
 ## Task: ${task.id}
@@ -1028,7 +1067,7 @@ ${task.dependencies.length > 0 ? `Dependencies: ${task.dependencies.join(", ")}`
 ## PROMPT.md
 
 ${task.prompt}
-${attachmentsSection}${commandsSection}${progressSection}
+${attachmentsSection}${commandsSection}${progressSection}${steeringSection}
 ## Review level: ${reviewLevel}
 
 ${reviewLevel === 0 ? "No reviews required. Implement directly." : ""}