policy: guard adoption baselines, resolve-time validation, and inherited-delta narration

Review fixes (ds-review-bot on #623):

- Persistence adoption compares the immutable policy baselines: onCreated's
  ownerless claim and adoptLivePrefix retain the STORED header, so a
  same-id live session with a conflicting baseline now rejects as a
  collision instead of appending under read-only and resuming under the
  stored danger-full-access.
- resolve() resolves the session override BEFORE applying an explicit
  approved mode: the one-shot grant no longer bypasses the unconditional
  durable-header validation.
- The approval narrator attributes positionally over the session's OWN
  events (past the seed boundary): a fork child whose baseline delta has
  no own override narrates 'inherited from the delegating session' instead
  of misattributing a stale seed-carried switch to the user or the
  operator.

Red-first: baseline-conflict adoption in the shared coordinator contract
(both backends), resolve-with-explicit-mode validation, and the fork-child
narration attribution case.

packages/sandbox/sandbox-policy/tests/policy.spec.ts

@@ -229,4 +229,13 @@ describe('delegation inheritance (overrideOf over the header baseline)', () => {
 
     expect(() => ctx.sandboxPolicy.overrideOf(child)).toThrow(/seedLength/)
   })
+
+  it('resolve() validates the durable header even when an explicit approved mode is supplied', async () => {
+    const ctx = await mounted()
+    const child = inheritedSession('sess-resolve-invalid', { sandboxMode: 'yolo' })
+
+    // The explicit one-shot grant must not become a validation bypass: the
+    // unconditional durable-header contract holds on EVERY resolution.
+    expect(() => ctx.sandboxPolicy.resolve({ session: child, mode: 'workspace-write' })).toThrow(/sandboxMode/)
+  })
 })