fix(heartbeat): reuse sessions across execution handoffs (#9917)

## Thinking Path

> - Paperclip uses durable task sessions so local adapters can resume
work across sequential heartbeat runs.
> - `execution_review_requested` and `execution_changes_requested` are
issue-local execution-policy handoffs, not new task assignments.
> - The existing `agent_task_sessions` lookup, adapter session codec,
workspace resolution, and effective config freshness checks already
decide whether reuse is safe.
> - Treating those two handoff wake reasons as unconditional
fresh-session boundaries discards a valid saved task session before
adapter resume can be attempted.
> - This makes Dev → CodeReview → Dev loops repeatedly cold-start even
when task, issue, agent, adapter, workspace, and config identity are
unchanged.
> - The fix is to let normal review/change-request handoffs reach the
durable task-session path while preserving explicit fresh-session and
unsafe-boundary resets.

## Linked Issues or Issue Description

Fixes #8246.

cc @cryppadotta — this is the narrow handoff-session policy change
discussed there: normal `execution_review_requested` /
`execution_changes_requested` wakes no longer force a fresh task session
by wake reason alone, while assignment, approval, review-participant
recovery, timer wakes, explicit `forceFreshSession`, and
config/workspace/model/session freshness still keep their safety
boundaries.

## What Changed

- Removed normal `execution_review_requested` and
`execution_changes_requested` from the unconditional task-session reset
policy.
- Kept fresh-session boundaries for:
  - `issue_assigned`
  - `execution_approval_requested`
  - `execution_review_participant_recovery`
  - `heartbeat_timer`
  - explicit `forceFreshSession`
  - existing config/model/workspace/session freshness reset paths
- Updated heartbeat session-policy tests so execution handoffs are
resume-eligible by wake reason alone.
- Preserved PF-4 timer-wake behavior and its explicit reset reason.

## Verification

- `npx pnpm@9.15.4 exec vitest run
server/src/__tests__/heartbeat-workspace-session.test.ts
server/src/__tests__/heartbeat-timer-wake-session-reset-pf4.test.ts
server/src/__tests__/codex-local-execute.test.ts
server/src/__tests__/issue-comment-reopen-routes.test.ts
--reporter=verbose` — 220 tests passed.
- `npx pnpm@9.15.4 --filter @paperclipai/server typecheck` — passed.
- `git diff --check` — passed.
- `coderabbit review --agent -t committed --base origin/master` — 0
findings.

## Risks

- Moderate behavior change in session-boundary policy: normal
review/change-request handoffs may now reuse a saved per-task session
when the existing identity/freshness checks pass.
- Safety boundaries remain in place for new assignments, approval gates,
review-participant recovery, timer/discovery wakes, explicit
fresh-session requests, and config/model/workspace/session drift.
- If a saved session is stale or incompatible, existing freshness/resume
fallback behavior still handles reset/fresh execution.

> For core feature work, check ROADMAP.md first and discuss it in #dev
before opening the PR. Feature PRs that overlap with planned core work
may need to be redirected — check the roadmap first. See
CONTRIBUTING.md.

## Model Used

OpenAI GPT-5.5. Tool use and local verification were enabled.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links
- [x] My branch name describes the change and contains no internal
Paperclip ticket ID
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes — N/A,
server policy/test-only change
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

Co-authored-by: santastabber <184111696+santastabber@users.noreply.github.com>

server/src/__tests__/heartbeat-timer-wake-session-reset-pf4.test.ts

@@ -30,17 +30,25 @@ describe("PF-4 shouldResetTaskSessionForWake", () => {
     ).toBe(false);
   });
 
-  it("still resets for the existing reset reasons", () => {
+  it("keeps assignment, approval, and review-participant recovery as fresh boundaries", () => {
     for (const wakeReason of [
       "issue_assigned",
-      "execution_review_requested",
       "execution_approval_requested",
-      "execution_changes_requested",
+      "execution_review_participant_recovery",
     ] as const) {
       expect(shouldResetTaskSessionForWake({ wakeReason })).toBe(true);
     }
   });
 
+  it("does not reset execution handoffs by wake reason alone", () => {
+    for (const wakeReason of [
+      "execution_review_requested",
+      "execution_changes_requested",
+    ] as const) {
+      expect(shouldResetTaskSessionForWake({ wakeReason })).toBe(false);
+    }
+  });
+
   it("still respects forceFreshSession === true", () => {
     expect(shouldResetTaskSessionForWake({ forceFreshSession: true })).toBe(true);
   });
@@ -80,19 +88,21 @@ describe("PF-4 describeSessionResetReason", () => {
     ).toBeNull();
   });
 
-  it("returns the existing reasons for the existing reset triggers", () => {
+  it("returns reasons for wake reasons that still force a fresh task session", () => {
     expect(describeSessionResetReason({ wakeReason: "issue_assigned" })).toBe(
       "wake reason is issue_assigned",
     );
-    expect(describeSessionResetReason({ wakeReason: "execution_review_requested" })).toBe(
-      "wake reason is execution_review_requested",
-    );
     expect(describeSessionResetReason({ wakeReason: "execution_approval_requested" })).toBe(
       "wake reason is execution_approval_requested",
     );
-    expect(describeSessionResetReason({ wakeReason: "execution_changes_requested" })).toBe(
-      "wake reason is execution_changes_requested",
-    );
+    expect(
+      describeSessionResetReason({ wakeReason: "execution_review_participant_recovery" }),
+    ).toBe("wake reason is execution_review_participant_recovery");
+  });
+
+  it("does not report review/change-request handoffs as reset reasons", () => {
+    expect(describeSessionResetReason({ wakeReason: "execution_review_requested" })).toBeNull();
+    expect(describeSessionResetReason({ wakeReason: "execution_changes_requested" })).toBeNull();
   });
 
   it("returns the forceFreshSession message when explicitly requested", () => {
@@ -116,6 +126,7 @@ describe("PF-4 describeSessionResetReason", () => {
       { wakeReason: "issue_assigned" },
       { wakeReason: "execution_review_requested" },
       { wakeReason: "execution_approval_requested" },
+      { wakeReason: "execution_review_participant_recovery" },
       { wakeReason: "execution_changes_requested" },
       { forceFreshSession: true },
       { wakeReason: "issue_commented" },

server/src/__tests__/heartbeat-workspace-session.test.ts

@@ -1791,16 +1791,16 @@ describe("shouldResetTaskSessionForWake", () => {
     expect(shouldResetTaskSessionForWake({ wakeReason: "issue_assigned" })).toBe(true);
   });
 
-  it("resets session context on execution review wakes", () => {
-    expect(shouldResetTaskSessionForWake({ wakeReason: "execution_review_requested" })).toBe(true);
+  it("preserves session context on execution review handoff wakes", () => {
+    expect(shouldResetTaskSessionForWake({ wakeReason: "execution_review_requested" })).toBe(false);
   });
 
   it("resets session context on execution approval wakes", () => {
     expect(shouldResetTaskSessionForWake({ wakeReason: "execution_approval_requested" })).toBe(true);
   });
 
-  it("resets session context on execution changes-requested wakes", () => {
-    expect(shouldResetTaskSessionForWake({ wakeReason: "execution_changes_requested" })).toBe(true);
+  it("preserves session context on execution changes-requested handoff wakes", () => {
+    expect(shouldResetTaskSessionForWake({ wakeReason: "execution_changes_requested" })).toBe(false);
   });
 
   it("preserves session context on timer heartbeats", () => {

server/src/services/heartbeat.ts

@@ -4122,10 +4122,8 @@ export function shouldResetTaskSessionForWake(
   const wakeReason = readNonEmptyString(contextSnapshot?.wakeReason);
   if (
     wakeReason === "issue_assigned" ||
-    wakeReason === "execution_review_requested" ||
     wakeReason === EXECUTION_REVIEW_PARTICIPANT_RECOVERY_WAKE_REASON ||
     wakeReason === "execution_approval_requested" ||
-    wakeReason === "execution_changes_requested" ||
     // PF-4: unscoped timer wakes are exploratory ("any new work?") and should
     // not accumulate low-value inbox scans. Issue-scoped timer wakes are
     // continuation work, so reuse their task session to avoid paying the full
@@ -4235,12 +4233,10 @@ export function describeSessionResetReason(
 
   const wakeReason = readNonEmptyString(contextSnapshot?.wakeReason);
   if (wakeReason === "issue_assigned") return "wake reason is issue_assigned";
-  if (wakeReason === "execution_review_requested") return "wake reason is execution_review_requested";
   if (wakeReason === EXECUTION_REVIEW_PARTICIPANT_RECOVERY_WAKE_REASON) {
     return `wake reason is ${EXECUTION_REVIEW_PARTICIPANT_RECOVERY_WAKE_REASON}`;
   }
   if (wakeReason === "execution_approval_requested") return "wake reason is execution_approval_requested";
-  if (wakeReason === "execution_changes_requested") return "wake reason is execution_changes_requested";
   // PF-4: paired with shouldResetTaskSessionForWake — keep the reason wording
   // explicit so run logs make session reuse/reset behavior legible.
   if (wakeReason === "heartbeat_timer" && !deriveTaskKey(contextSnapshot, null)) {