fix(ldf): invalidate stale selection cache

[zackees]

Closes#1094.\n\nBumps the LDF mode cache identity so cached selections from before sketch-rooted library discovery cannot keep stale framework sources in the build.\n\nValidation:\n- bash ./test -p fbuild-library-select\n- soldr cargo check -p fbuild-library-select -p fbuild-build-engine -p fbuild-build-arm\n- Fresh FastLED Blink teensy41 release build with current fbuild daemon; symbol audit reports no Audio, SdFat, SerialFlash, SDClass, or SD symbols.

Summary by CodeRabbit

• Bug Fixes
  • Updated library selection caching so outdated cached results are refreshed and recalculated when needed.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: c0e88a9e-f570-4bc6-9a1c-9accbb8e9a5f

📥 Commits

Reviewing files that changed from the base of the PR and between 0cedfaf and febcdd1.

📒 Files selected for processing (1)

• crates/fbuild-library-select/src/cache.rs

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📝 Walkthrough

Walkthrough

The library-selection cache key version changes from 3 to 4, causing entries generated with the previous version to be recomputed.

Changes

Library selection cache

Layer / File(s)	Summary
Invalidate stale resolver entries crates/fbuild-library-select/src/cache.rs	LDF_MODE_VERSION is incremented from 3 to 4, invalidating library-selection cache entries created under the previous version.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related issues

• feat(ldf): evaluate active preprocessor branches during library selection #1098 — The version bump supports updating library-selection cache keys for LDF preprocessing modes.

Possibly related PRs

• FastLED/fbuild#1097 — Related LDF framework-library selection changes also update cache versioning.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title is concise and accurately summarizes the cache invalidation change.
Linked Issues check	✅ Passed	The LDF mode version bump invalidates stale resolver cache entries, which matches the reported stale self-selection behavior.
Out of Scope Changes check	✅ Passed	Only the cache identity version changed, so no unrelated scope creep is present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/ldf-cache-mode-invalidation

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