perf: use incremental chat message fingerprinting

[charlesrhoward]

Summary

• replace full-history JSON fingerprinting with lightweight incremental metadata fingerprinting
• fingerprint now keys off message count and latest message metadata/part profile

Validation

• pnpm build

Closes #28

---

Note

Low Risk
Localized performance change in sync change-detection; main risk is missing updates when older messages change or metadata is absent, potentially delaying a save.

Overview
Replaces the chat history change-detection fingerprint from a full JSON.stringify of all messages to a lightweight string based on message count plus the latest message’s id/role/timestamp and a summary of its parts (text length, file/reasoning counts).

This reduces repeated serialization cost during local/cloud persistence and invalidation logic, while keeping behavior centered on detecting changes to the most recent message state.

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Project	Deployment	Actions	Updated (UTC)
drawit	Ready	Preview, Comment	Feb 21, 2026 9:55pm

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Include tool invocation state in message fingerprint

This fingerprint only tracks message count plus coarse metadata from the last message (text length and part counts), so updates to tool-invocation parts are not detected when their count stays the same. In this component, addToolResult(...) mutates existing tool-call parts in place; if the tool state/output changes but lengths/counts do not, usePersistMessagesOnChange treats the chat as unchanged and skips cloud/local persistence, which can leave restored sessions with stale or incomplete tool-call state.

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[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

^{Bugbot Autofix is ON. A Cloud Agent has been kicked off to fix the reported issues.}

[cursor]

Bugbot Autofix prepared fixes for 2 of the 2 bugs found in the latest run.

• ✅ Fixed: Fingerprint ignores all messages except the last one
  • The fingerprint now includes a joined list of all message IDs so earlier-message changes alter the persistence key.
• ✅ Fixed: Reasoning streaming progress invisible to fingerprint
  • The fingerprint now accumulates reasoning text length, so reasoning-delta growth triggers save detection during streaming.