Address review: the generate event resolves the agent target it serves

A winning overlay could reload after handleGo() minted a session but
before its result post landed. The close released its lease, the
server replayed the still-pending target, and another tab (or the
reloaded page, once it abandoned the unknown session) could claim it
and fire a second Go for a request that already had a session.

The overlay now names the target on the generate event it fires for it
(`agentTarget: {targetId, result}`, the same result it posts), and the
helper resolves the pending request the moment that event is accepted,
stripping the envelope before journaling. Whichever of the event and
the result post lands first answers; a page that dies between Go and
its result cannot leave the request pending, and a request whose event
never reached the helper is served exactly once by the rescuer.

Tests: a Rust integration case and a Node protocol case (claim, Go
event without a result post, verdict carries the session, a late claim
finds nothing pending, the journal carries no envelope), contract pins
for the handoff, and the contract doc.

Written with AI assistance (Claude).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/CLI-CONTRACT.md

@@ -1480,7 +1480,7 @@ Binds `127.0.0.1:PORT`. CORS: if request has `Origin` and (origin is loopback ht
 | `POST /manual-edit-discard?token=&pageUrl=` | 401 | see 10 |
 | `POST /manual-edit` | | 410 `{"error":"/manual-edit is removed; use /manual-edit-stash and /manual-edit-commit for staged copy edits."}` |
 | `POST /agent-target` | body JSON `token` mismatch → 401 `{"error":"Unauthorized"}`; invalid JSON → 400 `{"error":"Invalid JSON"}` | Agent-initiated targeting (the `generate` command). Validation (400 `{"error":<msg>}`, messages verbatim): `agent_target: selector is required`, `agent_target: selector too long` (>1000 chars), `agent_target: invalid action (valid: <VISUAL_ACTIONS joined ', '>)`, `agent_target: count must be 1-8`, `agent_target: text must be a string of at most 500 chars`, `agent_target: index must be a positive integer (1-based)`, `agent_target: prompt must be a string of at most 2000 chars`, `agent_target: dryRun must be a boolean`. No SSE client → 200 `{ok:false, error:'no_browser_connected'}`. Otherwise mint an 8-hex `targetId`, broadcast `agent_target` (see 6.2), and **hold the response** until `/agent-target-result` resolves it, every connected overlay has declined (busy roll call, see `/agent-target-claim`), or `IMPECCABLE_AGENT_TARGET_TIMEOUT_MS` (default 15000) elapses: busy verdict `{ok:false, error:'busy', state, reason}` from the first report when any report exists, else `{ok:false, error:'browser_timeout', timeoutMs}`. The held reply is 200 `{targetId, ...result}`; shutdown resolves every held request with `{ok:false, error:'server_stopping'}`. |
-| `POST /agent-target-result` | 401 / 400 Invalid JSON | `targetId` (non-empty string) required else 400 `{"error":"agent_target_result: missing targetId"}`; the remaining body fields (minus `token`) resolve the held request; 200 `{ok:true, delivered:boolean}` (`delivered:false` when nothing awaits that id). |
+| `POST /agent-target-result` | 401 / 400 Invalid JSON | `targetId` (non-empty string) required else 400 `{"error":"agent_target_result: missing targetId"}`; the remaining body fields (minus `token`) resolve the held request; 200 `{ok:true, delivered:boolean}` (`delivered:false` when nothing awaits that id). A `generate` event on `POST /events` may carry `agentTarget: {targetId, result}`: once the event is accepted, the server resolves that pending target with `result` (the envelope is stripped before journaling and never reaches the poller), so a page that dies between Go and its result cannot leave the request pending for a second Go elsewhere; whichever of the event and the result post lands first answers. |
 | `POST /agent-target-claim` | 401 / 400 Invalid JSON | `targetId` and `clientId` (non-empty strings) required else 400 `{"error":"agent_target_claim: missing targetId or clientId"}`. Roll call plus a first-wins lease, so exactly one overlay acts on a broadcast target. Unknown or resolved target → `{ok:true, granted:false, pending:false}` (ends a rescuer's retry loop). `eligible !== true` → record `{state, reason, result?}` under `clientId` (replacing an earlier report; `result` is the overlay's resolution verdict when `reason` is `no_match`, i.e. its page cannot resolve the selector), release the lease if this client holds it, answer `{ok:true, granted:false, pending}` (`pending` false once the request resolved, so a declining overlay knows whether to keep watching for a change of its word), then complete the roll call when no owner holds the lease and reports ≥ connected overlays. Verdict precedence: a report whose `reason` is not `no_match` (a tab that could serve later) → `{ok:false, error:'busy', state, reason}` at once; when every report is `no_match` the roll call stays open for `IMPECCABLE_AGENT_TARGET_RESOLVE_GRACE_MS` (default 3000) after each overlay's first such report (a late reporter extends the grace by the full window; a page whose element mounts late keeps re-checking while its decline answers `pending:true`, an eligible claim drops its stale report, and the overlay declines rather than posting a result when the element is gone after its claim), then answers the first report's `result` (e.g. `no_match` with `rawMatchCount`, `invalid_selector`); the timeout uses the same precedence when any report exists. `eligible === true` → drop this client's earlier report; `granted` when no owner, the same owner (renew), or the lease lapsed (`IMPECCABLE_AGENT_TARGET_CLAIM_LEASE_MS`, default 3000); answer `{ok:true, granted, pending:true}`. |
 | anything else | | 404 `Not found` |