fix: alert again when a change watch returns to a seen page

[Mrdifferent2022]

Problem

A watch with condition change keys its dedup notice on the page content hash alone. When a page oscillates A→B→A, the return to A produces a notice key that already exists, so insertIfAbsent silently swallows the alert and the user is never told the page changed back.

Commit 96c2525 fixed exactly this clears-and-reappears case for contains/price_below by committing an alertSequence with the outcome; the change branch was left content-hash-keyed.

Fix

• Increment alertSequence for every notification-worthy observation, including change.
• Key the notice on sequence:hash for all conditions, so a change back to previously seen content is a new alert while outcome-replay retries still deduplicate on the same committed key.

Verification

• New regression scenario in tests/monitor-recovery.test.ts: change with pages A→B→A→B alerts exactly 3 times; unchanged repeats stay quiet.
• Updated the count in tests/agent-api.test.ts (a change back to a seen page now alerts; identical consecutive checks still deduplicate).
• Full suite passes locally. Untested paths: none, sample-mode engine behavior is fully covered by existing fixtures.

Co-authored-by: Claude noreply@anthropic.com

[jerelvelarde]

Value: change watches alert again for A→B→A while outcome replay still deduplicates against a persisted sequence. Twenty-nine monitor-recovery/agent API tests passed. Template: problem, behavior, checks and sample-path limits are stated. Updated-main diff reviewed; no actionable security/correctness findings. Merge after required CI.