enrich: start the branch cache refresh in its own session

[m4ttheweric]

rt cd: the background cache refresh leaves the shell's process group

rt cd runs inside the shell's $(...), which shares the shell's process group. With a warm branch cache, the picker kicks off a background revalidation (spawnCacheRefresh) that stayed in that group for its whole GitLab/Linear round trip. herdr counts it as the pane's foreground job, so flock's launcher, which waits for the pane to go idle after rt cd, came back 10 to 15 seconds late.

What changed

• spawnCacheRefresh spawns with detached: true, as rt's other background spawns (trash.ts, prune.ts, user-path.ts) already do.
• Options moved into cacheRefreshSpawnOptions() so a test can pin them.

Verification

• New enrich-refresh-detached.test.ts; the enrich suite (35 tests) passes.
• Probed by hand: an unref'd Bun.spawn child inside $(...) stays in the shell's pgid; with detached: true it gets its own.

🤖 Generated with Claude Code

https://claude.ai/code/session_01LW34UkBwoPSwp672E7Bh3Y

Summary by CodeRabbit

• Bug Fixes
  • Cache refreshes now run independently of the terminal session that starts them, rather than being tied to its foreground process group. Refresh output no longer appears in the terminal, while the existing runtime environment is preserved. This helps refreshes continue without interfering with terminal activity.

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📝 Walkthrough

Walkthrough

The cache refresh spawn options now come from an exported helper. The helper preserves the child environment, ignores all three stdio streams, and sets detached mode. A test checks these option values.

Changes

Cache refresh process spawning

Layer / File(s)	Summary
Define and validate spawn options lib/enrich.ts, lib/__tests__/enrich-refresh-detached.test.ts	spawnCacheRefresh uses options returned by cacheRefreshSpawnOptions(). The helper sets the child environment, ignored stdio, and detached: true. The test checks these values.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 2a18b

The cache refresh is configured to run detached, and the focused test checks its spawn options. No actionable merge-blocking risk is evidenced; the PR is ready for normal checks.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: spawning the branch cache refresh in its own session.

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