feat(boulder-state): add session_origins tracking for direct vs appended sessions

- Add session_origins field to BoulderState type
- Track direct vs appended session origins in storage layer
- Add migration logic for existing state files
- Add comprehensive tests for session origin tracking

🤖 Generated with assistance of OhMyOpenCode

src/features/boulder-state/storage.test.ts

@@ -118,6 +118,40 @@ describe("boulder-state", () => {
       expect(result!.session_ids).toEqual([])
     })
 
+    test("should backfill missing origin as direct only for a single tracked session", () => {
+      // given
+      const boulderFile = join(SISYPHUS_DIR, "boulder.json")
+      writeFileSync(boulderFile, JSON.stringify({
+        active_plan: "/path/to/plan.md",
+        started_at: "2026-01-01T00:00:00Z",
+        session_ids: ["session-1"],
+        plan_name: "plan",
+      }))
+
+      // when
+      const result = readBoulderState(TEST_DIR)
+
+      // then
+      expect(result?.session_origins).toEqual({ "session-1": "direct" })
+    })
+
+    test("should keep missing origins empty when multiple sessions are tracked", () => {
+      // given
+      const boulderFile = join(SISYPHUS_DIR, "boulder.json")
+      writeFileSync(boulderFile, JSON.stringify({
+        active_plan: "/path/to/plan.md",
+        started_at: "2026-01-01T00:00:00Z",
+        session_ids: ["session-1", "session-2"],
+        plan_name: "plan",
+      }))
+
+      // when
+      const result = readBoulderState(TEST_DIR)
+
+      // then
+      expect(result?.session_origins).toEqual({})
+    })
+
     test("should read valid boulder state", () => {
       // given - valid boulder.json
       const state: BoulderState = {
@@ -239,6 +273,26 @@ describe("boulder-state", () => {
       expect(result).not.toBeNull()
       expect(result!.session_ids).toContain("ses-new")
     })
+
+    test("should persist appended session origin when provided", () => {
+      // given
+      writeBoulderState(TEST_DIR, {
+        active_plan: "/path/to/plan.md",
+        started_at: "2026-01-02T10:00:00Z",
+        session_ids: ["session-1"],
+        session_origins: { "session-1": "direct" },
+        plan_name: "plan",
+      })
+
+      // when
+      const result = appendSessionId(TEST_DIR, "session-2", "appended")
+
+      // then
+      expect(result?.session_origins).toEqual({
+        "session-1": "direct",
+        "session-2": "appended",
+      })
+    })
   })
 
   describe("clearBoulderState", () => {
@@ -547,6 +601,18 @@ describe("boulder-state", () => {
       expect(state.plan_name).toBe("feature")
     })
 
+    test("should mark the initial session origin as direct", () => {
+      // given
+      const planPath = "/path/to/feature.md"
+      const sessionId = "ses-origin"
+
+      // when
+      const state = createBoulderState(planPath, sessionId)
+
+      // then
+      expect(state.session_origins).toEqual({ [sessionId]: "direct" })
+    })
+
     test("should allow agent to be undefined", () => {
       //#given - plan path and session id without agent
       const planPath = "/path/to/legacy.md"

src/features/boulder-state/storage.ts

@@ -31,6 +31,19 @@ export function readBoulderState(directory: string): BoulderState | null {
     if (!Array.isArray(parsed.session_ids)) {
       parsed.session_ids = []
     }
+    if (!parsed.session_origins || typeof parsed.session_origins !== "object" || Array.isArray(parsed.session_origins)) {
+      parsed.session_origins = {}
+    }
+    if (parsed.session_ids.length === 1) {
+      const soleSessionId = parsed.session_ids[0]
+      if (
+        typeof soleSessionId === "string"
+        && parsed.session_origins[soleSessionId] !== "appended"
+        && parsed.session_origins[soleSessionId] !== "direct"
+      ) {
+        parsed.session_origins[soleSessionId] = "direct"
+      }
+    }
     if (!parsed.task_sessions || typeof parsed.task_sessions !== "object" || Array.isArray(parsed.task_sessions)) {
       parsed.task_sessions = {}
     }
@@ -56,23 +69,41 @@ export function writeBoulderState(directory: string, state: BoulderState): boole
   }
 }
 
-export function appendSessionId(directory: string, sessionId: string): BoulderState | null {
+export function appendSessionId(
+  directory: string,
+  sessionId: string,
+  origin: "direct" | "appended" = "direct",
+): BoulderState | null {
   const state = readBoulderState(directory)
   if (!state) return null
 
+  if (!state.session_origins || typeof state.session_origins !== "object" || Array.isArray(state.session_origins)) {
+    state.session_origins = {}
+  }
+
   if (!state.session_ids?.includes(sessionId)) {
     if (!Array.isArray(state.session_ids)) {
       state.session_ids = []
     }
     const originalSessionIds = [...state.session_ids]
+    const originalSessionOrigins = { ...state.session_origins }
     state.session_ids.push(sessionId)
+    state.session_origins[sessionId] = origin
     if (writeBoulderState(directory, state)) {
       return state
     }
     state.session_ids = originalSessionIds
+    state.session_origins = originalSessionOrigins
     return null
   }
 
+  if (!state.session_origins[sessionId]) {
+    state.session_origins[sessionId] = origin
+    if (!writeBoulderState(directory, state)) {
+      return null
+    }
+  }
+
   return state
 }
 
@@ -213,6 +244,9 @@ export function createBoulderState(
     active_plan: planPath,
     started_at: new Date().toISOString(),
     session_ids: [sessionId],
+    session_origins: {
+      [sessionId]: "direct",
+    },
     plan_name: getPlanName(planPath),
     ...(agent !== undefined ? { agent } : {}),
     ...(worktreePath !== undefined ? { worktree_path: worktreePath } : {}),

src/features/boulder-state/types.ts

@@ -12,6 +12,7 @@ export interface BoulderState {
   started_at: string
   /** Session IDs that have worked on this plan */
   session_ids: string[]
+  session_origins?: Record<string, "direct" | "appended">
   /** Plan name derived from filename */
   plan_name: string
   /** Agent type to use when resuming (e.g., 'atlas') */