Pin plugin Runner cleanup to its physical task (#19300)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work.
> - Plugin Runner owners manage a physical task through an environment
lease.
> - The existing replacement path can assign a new physical task to that
same lease.
> - A delayed old owner can then stop the replacement or mark it
stopped.
> - Cleanup must keep the original physical task identity across RPC and
database writes.
> - This pull request pins that identity and keeps cleanup available to
the new owner.

## Linked Issues or Issue Description

Refs #19134 and #19157. This fix is based on master and does not enable
repeated stopped-source recovery. A search found no duplicate fix.

**What happened?**

The maintained `createOwnedSandbox` replacement path changes
`providerLeaseId` on one lease. An old task owner uses that mutable
lease for a later Stop. A stopped-state response already in flight can
also update the new task's flags.

**Expected behavior**

The old owner must address its original task. Its late cleanup writes
must not alter the replacement. The replacement's own owner must still
stop and complete it.

**Steps to reproduce**

1. Create a plugin task owner for a stopped task.
2. Replace that task through the existing describe/startup path on the
same lease.
3. Resume an old checkpoint or a held old status response.
4. Observe a Stop for the replacement or an incorrect stopped flag
before this fix.

## What Changed

- Require each task owner to keep the physical ID returned by its
description. Reject a rebind to a different task.
- Carry the ID through the existing internal task context after startup
ends. Reject a changed physical task before RPC dispatch.
- Match the physical task in stopped-state, completion and
credential-handoff writes.
- Hold the exact lease row through the retained-session database update
and local checkpoint save.
- Cover the maintained replacement path with real PostgreSQL tests.
Preserve positive cleanup for the replacement owner. Document this
boundary.

## Verification

- Both replacement regressions failed on unmodified master `10a7d039c8`:
delayed old-owner Stop targeted the replacement, and a held old status
response marked it stopped.
- Six focused files passed 160 tests: task authority, task runtime, warm
tasks, execution target, credential writeback and task owner.
- Four selected executor factory cases passed. They cover task-only
providers and the physical task binding after the startup context ends.
- Runner TypeScript, plugin SDK and adapter-utils builds passed. Server
TypeScript check passed. Diff and added-line secret scans passed.
- All 15 setup-probe cases passed with the actual Runner and fake
provider binaries. The first local attempt lacked cargo on PATH. A
sandboxed native attempt timed out in seven process cases; the unchanged
run with loopback permission passed all 15. A separate initial DB
integration attempt was denied a loopback listener; its
permission-correct run passed.
- Review found three missed constructors in the existing SDK/Core
lifecycle fixture. They now use the actual describe result. All four
cases in that real PostgreSQL and worker RPC file passed.
- The first GitHub attempt failed in the unchanged GitHub recovery
pagination case in `chat-channels.integration.test.ts`: its zero-request
assertion observed a configuration GET. That exact case passed locally
without code or assertion changes. The one failed-job-only retry passed;
the initial failure log is retained.
- [GitHub workflow
42082587576](https://github.com/paperclipai/paperclip/actions/runs/42082587576)
passed on its second attempt. All CI checks completed, and Snyk passed.
Standard Greptile scored exact head `fb914d98b99e` 5/5 with no
unresolved threads. The branch is mergeable and ready for review.

## Risks

The task context change is internal. It adds no plugin wire field,
schema or Runner mode. A stale owner now gets an error and cannot clean
up a replacement. A new owner can still clean up that task. The retained
checkpoint write holds one existing lease row during a bounded local
file write.

Repeated stopped-source incarnation admission, runtime pins and
deployments are outside this change.

## Model Used

OpenAI GPT-6.1 Sol (`gpt-6.1-sol`), high reasoning. Used repository
tools, TypeScript and real PostgreSQL tests.

## 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 described the issue in-PR using the bug template
- [x] I have not referenced internal or instance-local Paperclip issues
or links
- [x] My branch name describes the change
- [x] I have run the focused tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation
- [x] I have considered and documented risks
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no unresolved findings
- [x] I will address reviewer comments before requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

server/src/services/native-runtime/native-session-executor.test.ts

@@ -13430,6 +13430,33 @@ describe("runnerd provider runtime wiring", () => {
     return state.createTransport.mock.calls[0]![0].stateDirectory!;
   }
 
+  it("keeps physical task cleanup binding after the startup context finishes", async () => {
+    const current = scopedNativeExecution("physical-task-cleanup");
+    const context = new NativeExecutionContext(current, 1_000);
+    const owner = vi.spyOn(pluginTaskRuntime, "createPluginRunnerTaskOwner");
+    const db = leaseDb(current), update = db.update.bind(db);
+    db.update = ((table: unknown) => table === environmentLeases
+      ? { set: () => ({ where: () => ({ returning: async () => [] }) }) }
+      : update(table as never)) as typeof db.update;
+    db.transaction = (async callback => callback(db as never)) as typeof db.transaction;
+    const task = vi.fn(async (_operation: unknown, _options?: { executionContext?: unknown; expectedTaskId?: string }) => ({
+      kind: "description", taskId: "physical-task", launchPreparationVersion: 1, projectAuthCheckVersion: 1,
+      runner: { version: "fixture", digest: `sha256:${"a".repeat(64)}` },
+    }));
+    try {
+      await createRunnerdBackend({ db, execution: current, runnerInstanceId: "physical-task-runner",
+        executionContext: context, runnerIngressAuthorized: true, runnerExecutionTarget: {
+          kind: "remote", transport: "sandbox", remoteCwd: ".", leaseId: "lease", runnerTask: task,
+        } });
+      const input = owner.mock.calls.at(-1)![0];
+      expect(input.taskId).toBe("physical-task");
+      context.finish();
+      await input.task({ kind: "stop" }, { expectedTaskId: "physical-task" });
+      expect(task).toHaveBeenLastCalledWith({ kind: "stop" }, { expectedTaskId: "physical-task" });
+      await expect(input.onSessionRetained!({})).rejects.toThrow("physical task changed");
+    } finally { context.finish(); owner.mockRestore(); }
+  });
+
   it("rejects a late backend factory after its startup context has finished", async () => {
     const current = scopedNativeExecution("late-context-factory");
     state.createBackend.mockClear();