feat: harden chat history and add tests

[Eruis2579]

Summary

Hardens chat history utilities with history limits and adds test coverage for history-context and long-term-chat-history.

Changes

buildHistoryContext (history-context.ts)

• Introduced BuildHistoryContextParams interface for a clearer API
• Added optional historyLimit parameter (default DEFAULT_HISTORY_LIMIT, 10)
• When historyLimit > 0, only the last N entries are used in the prompt
• When historyLimit <= 0, all entries are included (no trimming)

LongTermChatHistory (long-term-chat-history.ts)

• Added maxEntries (default 200) to cap stored messages
• Constructor now accepts optional options?: { maxEntries?: number }
• load(): rewrites file on parse error and trims to maxEntries if needed
• addUserMessage(): trims messages to maxEntries after adding a new entry
• Avoids unbounded growth of .dexter/messages/chat_history.json

Tests

• history-context.test.ts: Tests empty history, formatting, markers, custom line breaks, default limit, explicit historyLimit override, and disabling limit with historyLimit <= 0
• long-term-chat-history.test.ts: Tests creation of history file, stack ordering, updateAgentResponse, deduplication in getMessageStrings, maxEntries on add, and trimming on load

Backward Compatibility

• Existing buildHistoryContext({ entries, currentMessage }) calls behave as before (default limit of 10)
• Existing LongTermChatHistory(baseDir) usage is unchanged (default maxEntries of 200)

Testing

bun test

[Eruis2579]

Hi, @virattt, Could you review my PR, Please?

[Eruis2579]

Hi, @virattt, Could you review my PR, Please?

[Eruis2579]

@virattt, Please review my PR. Thank you

[Eruis2579]

@virattt, Please review my PR. Thank you

[virattt]

Thanks for the contribution — nice additions, especially the test coverage and the maxEntries cap on LongTermChatHistory. I spotted a couple of issues worth fixing before we merge.

buildHistoryContext default limit silently halves context

The new DEFAULT_HISTORY_LIMIT (10) in buildHistoryContext counts entries, but the same constant is already used by InMemoryChatHistory.getRecentTurns() to limit turns. Each turn produces two entries (user + assistant), so:

1. getRecentTurns(10) → up to 20 HistoryEntry items
2. buildHistoryContext now slices to the last 10 entries → 5 turns

The call in agent.ts doesn't pass historyLimit, so it picks up the default and quietly drops half the conversation context. Easiest fix is probably to pass historyLimit: 0 at that call site, or remove the default from buildHistoryContext entirely and let callers opt in.

maxEntries doc says <= 0 means "no limit", code says otherwise

The JSDoc on the constructor option says values <= 0 are treated as "no limit", but the implementation falls through to DEFAULT_MAX_ENTRIES (200):

this.maxEntries =
  typeof requestedMax === 'number' && requestedMax > 0
    ? Math.floor(requestedMax)
    : DEFAULT_MAX_ENTRIES;

Either update the doc or add a code path that actually disables trimming when <= 0 is passed.

save() on parse error overwrites corrupt file

Currently, a corrupt chat_history.json just resets in-memory state without touching the file — users could still recover manually. The PR adds await this.save() in the catch block, which silently replaces the file with []. This is a judgment call, but worth being intentional about.

Minor style nits

• Both test files end the describe block with }) instead of }); (project uses semicolons everywhere).
• The PR changes .map(entry => to .map((entry) => in history-context.ts — the rest of the codebase uses the no-parens style for single params.
• The long-term history test writes to a relative .dexter-long-term-history-tests dir; os.tmpdir() would be more robust.

---

Issue	Severity
Default historyLimit halves agent context	Bug — needs fix
maxEntries doc/code mismatch	Minor bug
save() on corrupt file	Design choice, worth discussing
Semicolons / arrow parens / test dir	Nit