## Summary
PCH and PCM artifacts are now cached to disk at
`.clice/cache/{pch/,pcm/}` with content-addressed filenames, so they
survive server restarts. Dependency metadata is persisted in
`cache.json` (using eventide serde) with a shared path table for
deduplication.
### Key changes
- **protocol.h**: `output_path` field on `BuildPCHParams` /
`BuildPCMParams` so master specifies where workers write
- **stateless_worker.cpp**: Atomic write via `.tmp` + `fs::rename`;
`CompilationUnit` destroyed before rename to flush the file to disk;
fallback to temp file when `output_path` is empty (unit tests)
- **master_server.h**: `PCMState` struct, `pcm_states` map,
`load_cache()` / `save_cache()` / `cleanup_cache()` methods
- **master_server.cpp**: Cache lifecycle — load from `cache.json` on
startup, save after each PCH/PCM build and on exit; deterministic path
computation (`xxh3` preamble hash for PCH, module name + source path
hash for PCM); stale files (>7 days) cleaned on startup; `cache.json`
uses shared path table to avoid redundant storage of header paths across
entries
- **filesystem.h**: `fs::rename()` helper; `ThreadSafeFS` broadened to
match `.pch` extension instead of `preamble-` prefix
- **tests**: 11 new integration tests covering PCH/PCM persistence,
cross-session reuse, staleness detection, shared preamble dedup, and
restart survival; unit tests updated with `output_path`
### Naming scheme
- **PCH**: `.clice/cache/pch/<016x(xxh3(preamble))>.pch`
- **PCM**:
`.clice/cache/pcm/<module_name>-<016x(xxh3(source_path))>.pcm`
## Test plan
- [x] Unit tests — 448 passed
- [x] Integration tests — 92 passed (including 11 new persistent cache
tests)
- [x] Smoke tests — 1 passed
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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