perf(desktop): reduce terminal memory footprint

[saddlepaddle]

Summary

• Reduce default terminal scrollback from 10,000 to 5,000 lines, saving ~1.6MB per terminal session (both renderer xterm and daemon headless emulator)
• Extract scrollback default to shared constant DEFAULT_TERMINAL_SCROLLBACK for future configurability
• Clear emulator scrollback buffer before dispose for immediate memory release instead of relying on GC

Test plan

• Typecheck passes
• All 735 tests pass
• Lint clean
• Verify terminal scrollback still works (scroll up through history)
• Verify terminal dispose doesn't cause errors on tab close

Summary by CodeRabbit

• Changes
  • Default terminal scrollback reduced to 5,000 lines (now driven by a shared constant).
  • Improved terminal disposal to proactively clear buffers and free memory.

[coderabbitai]

📝 Walkthrough

Walkthrough

The pull request centralizes previously hard-coded terminal scrollback values into a new exported constant DEFAULT_TERMINAL_SCROLLBACK = 5000, updates usages across main and renderer code to reference the constant, and adds a proactive clear during headless terminal disposal. No public APIs or exported signatures were changed.

Changes

Cohort / File(s)	Summary
Shared Constants apps/desktop/src/shared/constants.ts	Add exported DEFAULT_TERMINAL_SCROLLBACK = 5000.
Main process terminal code apps/desktop/src/main/lib/terminal-host/headless-emulator.ts, apps/desktop/src/main/lib/terminal/session.ts, apps/desktop/src/main/terminal-host/session.ts	Replace magic 10000 scrollback defaults with DEFAULT_TERMINAL_SCROLLBACK; add clearing of headless terminal before dispose; update snapshot serialization and constructor options.
Renderer terminal config apps/desktop/src/renderer/screens/main/components/WorkspaceView/ContentView/TabsContent/Terminal/config.ts	Change TERMINAL_OPTIONS.scrollback from 10000 to DEFAULT_TERMINAL_SCROLLBACK.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• feat(desktop): use headless xterm for terminal scrollback storage #686 — Touches headless terminal / scrollback implementation and may overlap with disposal or scrollback behavior changes.
• implement more font and xterm rendering improvements #324 — Modifies TERMINAL_OPTIONS.scrollback and centralization of scrollback defaults in renderer config.

Poem

🐇 I nibbled the magic number down to five K,
I hopped through code paths to tuck it away.
A shared little constant, tidy and neat,
No more scattered numbers on every seat.
Hooray for clean defaults — let memory sleep sweet!

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and accurately summarizes the main change: reducing terminal memory footprint through configuration adjustments.
Description check	✅ Passed	The description provides a clear summary of changes, test results, and pending manual tests, but is missing the formally structured template sections.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into main

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fly-alerts

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No actionable comments were generated in the recent review. 🎉

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