fix(vscode): bound sync filter state

[marius-kilocode]

What Problem This Solves

The shared VS Code connection receives both normal live events and compatibility sync envelopes for several session, message, and message-part events. PR #13410 suppresses a matching sync envelope after the same live event has been delivered.

The first follow-up implementation introduced two edge cases in that tracking state:

• It could stop recording new live event IDs after the tracking set reached its cap, so duplicate suppression stopped during sustained event bursts.
• The tracking state needed to be scoped to one SSE connection so IDs from a previous connection could not affect a reconnect.

Why This Change Was Made

Use a bounded sliding window for recently delivered live event IDs. When the 1,024-entry cap is reached, the oldest ID is evicted and the new live ID is tracked. Promptly arriving compatibility envelopes continue to be deduplicated. If an envelope arrives after its live ID has left the bounded window, it is forwarded instead of being incorrectly suppressed.

Create the filter inside doConnect() so each SdkSSEAdapter connection has independent state. Reconnects and server restarts cannot reuse stale IDs.

User Impact

The duplicate-event optimization continues to reduce downstream processing across the VS Code sidebar, editor tabs, and Agent Manager. Delayed or replay-only compatibility events remain deliverable, and reconnects do not carry stale deduplication state.

Event scenario	Behavior
Matching live event and prompt sync envelope	Suppress the duplicate envelope
Matching envelope after the 1,024-entry window	Forward the envelope
Replay-only sync event	Forward the event
Event ID from an earlier SSE connection	Do not reuse the ID
session.updated reconciliation envelope	Preserve the envelope

Evidence

Validation	Result
Focused event regression tests	88 passed
Sliding-window overflow behavior	Covered
Delayed envelope behavior	Covered
Connection lifecycle isolation	Covered
VS Code typecheck	Passed
VS Code lint	Passed
CI	Green

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• .changeset/fix-sync-filter-lifecycle.md
• packages/kilo-vscode/src/services/cli-backend/connection-service.ts
• packages/kilo-vscode/src/services/cli-backend/connection-utils.ts
• packages/kilo-vscode/tests/unit/connection-utils.test.ts

Previous Review Summary (commit 45695e6)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit 45695e6)

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• .changeset/fix-sync-filter-lifecycle.md
• packages/kilo-vscode/src/services/cli-backend/connection-service.ts
• packages/kilo-vscode/src/services/cli-backend/connection-utils.ts
• packages/kilo-vscode/tests/unit/connection-utils.test.ts

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_{Review guidance: REVIEW.md from base branch main}

[iscekic]

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