Address review: the server ends the resolution watch, and a reconnect re-participates

Two ways a page's word could go stale after the resolve-before-claim
change: an element that mounts later than the quick re-checks, and an
EventSource reconnect that did not overlap the old connection (the server
drops that page's word on the close, replays the target, and the replay
guard ignored it, so the roll call waited on a word that never came).

A decline's answer now carries pending, like a denied claim does, so a page
that could not resolve the target reports the miss after the quick
re-checks (the roll call can complete on the other overlays' words) and
keeps re-checking once a second for as long as the server says the request
is pending, claiming the moment the element mounts; the server drops the
stale report on an eligible claim and ends the watch by answering
pending:false once the request resolved or timed out. The overlay tracks
its participation per target: a replayed target is ignored only while this
page is acting on it, and is otherwise handled again, so a busy or
unresolvable page re-declines (idempotent) and an idle page claims.

Unit, protocol, and contract cases updated; the decline answers now say
whether the request is still pending.

AI-assisted: implemented and tested with Claude Code under maintainer
direction.

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

tests/live-browser-source.test.mjs

@@ -848,8 +848,13 @@ describe('live-browser source contracts', () => {
     );
     assert.match(
       SOURCE,
-      /function handleAgentTarget\(msg\) \{[\s\S]{0,120}?if \(agentTargetsSeen\.includes\(msg\.targetId\)\) return;/,
-      'a replayed target this page already handled must not start a second claim or Go',
+      /function handleAgentTarget\(msg\) \{[\s\S]{0,120}?if \(agentTargetsSeen\.get\(msg\.targetId\) === 'acting'\) return;/,
+      'a replayed target this page is acting on must not start a second claim or Go; any other replay is handled again',
+    );
+    assert.match(
+      SOURCE,
+      /if \(claim\.granted\) \{ noteAgentTarget\(msg\.targetId, 'acting'\); actOnAgentTarget\(msg\); return; \}/,
+      'a granted claim marks the target as acting before Go',
     );
     // A page that cannot resolve the target never claims it: a first-wins
     // claim would otherwise let the wrong page answer no_match for a target
@@ -871,8 +876,13 @@ describe('live-browser source contracts', () => {
     );
     assert.match(
       SOURCE,
-      /function retryAgentTargetResolution\(msg, attempt, lastError\) \{[\s\S]{0,200}?reason: 'no_match', result: lastError[\s\S]{0,600}?if \(!probe\.error\) \{ claimAndActOnAgentTarget\(msg\); return; \}/,
-      'the page claims the moment the element mounts, and reports only the last miss',
+      /function retryAgentTargetResolution\(msg, attempt, lastError\) \{[\s\S]{0,300}?reason: 'no_match', result: lastError[\s\S]{0,120}?if \(!answer\.pending\) return;[\s\S]{0,120}?watchAgentTargetResolution\(msg, lastError\)/,
+      'after the quick re-checks the page reports the miss and keeps watching while the server says the request is pending',
+    );
+    assert.match(
+      SOURCE,
+      /function watchAgentTargetResolution\(msg, lastError\) \{[\s\S]{0,400}?if \(!probe\.error\) \{ claimAndActOnAgentTarget\(msg\); return; \}[\s\S]{0,500}?if \(!answer\.pending\) return;/,
+      'a late mount turns into a claim, and the server ends the watch',
     );
     // The per-origin session cache must not let a tab on another page of
     // the app resume this page's session (it would sit in GENERATING for a
@@ -890,8 +900,8 @@ describe('live-browser source contracts', () => {
     );
     assert.equal(
       (SOURCE.match(/claimAndActOnAgentTarget\(msg\)/g) || []).length,
-      5,
-      'the first claim, the busy-to-idle re-claim, and the resolution re-check must share the rescue path (definition, three call sites, the retry)',
+      6,
+      'the first claim, the busy-to-idle re-claim, the resolution re-check, and the resolution watch must share the rescue path (definition, four call sites, the retry)',
     );
   });