Refine history persistence architecture

[merefield]

Summary

• make history writes atomic with temp-file-then-rename persistence
• move normal history saving onto explicit exit paths, keeping cleanup as a fallback
• warn when persisted history cannot be parsed or written, and repair normalized/invalid history on immediate exit
• stop persisting regenerated system messages and trim saved history by conversation turn
• rename the turn-retention setting to max_history_turns while keeping legacy max_history as a deprecated compatibility fallback
• extend Bats coverage for invalid history files, immediate repair-on-exit behavior, turn-based trimming, and the renamed config key

Verification

• make check

Fixes #12

[Copilot]

Pull request overview

Refactors CLAI’s cross-session history persistence to be more robust and intentional: atomic writes, explicit save points, warning on failures, and persisting a turn-trimmed conversation view rather than raw transcripts.

Changes:

• Add atomic history persistence (temp file + rename) with warnings on parse/write failures.
• Introduce max_history_turns (with deprecated max_history fallback) and trim persisted history by user-turn boundaries.
• Extend Bats coverage for invalid history repair, turn-based trimming, deprecation behavior, and ensuring system messages aren’t persisted.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
clai.sh	Implements atomic history writes, new max_history_turns config handling, history normalization/trimming, and explicit exit persistence.
test/smoke.bats	Updates configs to max_history_turns and adds tests for trimming behavior, legacy key warning, and invalid history handling.
README.md	Documents max_history_turns and deprecates max_history.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.