## Summary
Initial integration of `CompileGraph` (#375) into `MasterServer`,
enabling basic end-to-end C++20 module support: on-demand PCM building,
dependency-ordered compilation, cascade invalidation on save, and
diagnostic integration.
This is a **first-pass implementation** — the core pipeline works, but
there are known areas for follow-up:
- PCM files go to system temp dir instead of `.clice/cache/`; no disk
cleanup on invalidation
- `run_build_drain` scans imports itself rather than delegating fully to
CompileGraph
- No incremental/partial rebuild (full PCM rebuild on any change)
- Cycle detection is tested at unit level but integration-level coverage
is minimal
## Changes
### Module dependency compilation (`master_server.cpp`)
Before sending a file to the stateful worker, `run_build_drain` now:
1. Scans imports via `scan_precise()` to discover module dependencies
2. Compiles each dep through `compile_graph->compile()`, which
recursively builds transitive PCMs
3. Handles implementation units — `module M;` implicitly needs the
interface PCM
4. Passes all built PCMs to the stateful worker, excluding the file's
own PCM
5. Skips compile on dep failure and resets `build_running` /
`drain_scheduled`
6. Re-lookups iterators after `co_await` to avoid use-after-invalidation
### Cascade invalidation (`didSave` / `didClose`)
- `didSave`: calls `compile_graph->update()` to mark transitive
dependents dirty, removes stale PCM paths, schedules rebuilds for open
dirtied files
- `didClose`: cancels in-flight compilations for the closed file
### Other fixes in this PR
- Debounce timers switched to `shared_ptr` to prevent use-after-free
when `didClose` destroys the timer mid-wait
- `fill_compile_args` returns `bool`; callers handle empty CDB
gracefully
- Adapt all `PositionMapper` call sites to the new `optional` return API
from eventide
## Test plan
- [x] 25 C++ unit tests for CompileGraph (cycles, partial failure,
cancel, update, empty graph)
- [x] 24 C++ integration tests with real clang PCM compilation
- [x] 3 worker-level module tests (BuildPCM, PCM-dependent compile,
multi-module)
- [x] 26 Python LSP integration tests (single module through circular
deps, hover, error diagnostics)
- [x] 371 unit tests + 54 integration tests pass
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
