## Summary
Three pre-existing bugs cause worker processes to crash with SEGV or
SIGABRT. On the main branch these crashes are silent (workers die,
requests fail fast with "transport closed", tests still pass because
null responses are accepted). However when combined with #432's worker
respawn mechanism, the crash-respawn-crash cycle on low-core CI machines
causes request timeouts and smoke test hangs.
### Fixes
- **compilation.cpp**: `ProxyAction::CreateASTConsumer` now checks for
null before passing to `MultiplexConsumer`. When the wrapped action's
`CreateASTConsumer` fails (e.g. missing system headers during PCH
generation), this previously caused a null pointer dereference, SEGV,
ASAN kills the stateless worker.
- **compilation_unit.cpp**: `file_path()` returns empty `StringRef` on
invalid `FileID` instead of asserting. The assert fired when
`IncludeGraph::from()` called `file_path(interested_file())` on an AST
compiled with synthesized default commands (no compile_commands.json,
clang++ -std=c++20 fallback, no system headers, invalid main file ID),
SIGABRT, stateful worker crash.
- **compiler.cpp**: `ensure_pch` now creates the PCH cache directory
before sending the build request. Previously, when `load_workspace()`
exited early (no compile_commands.json), the cache subdirectories were
never created, causing every PCH write to fail with "No such file or
directory".
- **master_server.cpp/h**: `load_workspace()` changed from
`kota::task<>` to plain `void` -- it contains only synchronous
filesystem operations and no co_await, so the coroutine wrapper was
unnecessary. Called directly instead of via `loop.schedule()`.
## Test plan
- [x] Verified zero SEGV/SIGABRT/assertion crashes in worker stderr
after fix
- [x] rapid_edit.jsonl smoke test passes 3/3 runs consistently (34s
each)
- [x] Behavior matches main branch (both return 134 responses, 0
pending)
- [x] Debug build with ASAN (detect_leaks=0) -- clean run, no sanitizer
reports
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<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **Bug Fixes**
* Improved error handling for AST consumer creation with null checks and
a clear failure path.
* Safer file-path access that returns empty for invalid identifiers
instead of asserting.
* PCH cache handling now validates cache configuration, attempts
directory creation, logs warnings, and aborts PCH builds on failure.
* **Refactor**
* Workspace loading changed from asynchronous to synchronous execution.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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