[NOT READY FOR REVIEW] feat(dev): CodeZip dev runner and process lifecycle core

[tejaskash]

Second PR in the agentcore project dev stack, on top of #1880. This adds the machinery that actually runs an agent locally — nothing is user-visible yet; the dev handler wires it up in a later PR.

What changed

src/core/dev/ is new and has three pieces:

spawnServer (process.ts) owns process lifecycle for a long-running server: streams output line by line to a log callback, escalates SIGTERM → SIGKILL on stop, and registers a process-group reaper so a detached server can't outlive the CLI and squat on the port. The child is spawned detached (its own process group) on POSIX so stopping it also stops uvicorn's reload workers — killing just the parent leaves the worker holding the socket.

CodeZipDevRunner (codezip.ts) runs a CodeZip runtime from a resolved project. Python entrypoints get a uv-managed venv (uv sync on first run, skipped when uvicorn is already in .venv) and then uvicorn --reload. TypeScript entrypoints get npm install + tsx watch. The agent process receives PORT and LOCAL_DEV=1 plus whatever env the caller passes — .env.local loading comes with the handler PR.

The DevRunner interface lives in handlers/project/dev/types.ts next to its future consumer, following the repo's dependency-inversion rule. The runner takes injectable run/spawn seams, so its tests never start real uv or uvicorn; the process tests use real short-lived node -e processes, since process handling is the thing under test there.

One deliberate duplication: run.ts carries the same CommandRunner shape as src/io/exec.ts from #1872. Whichever lands second folds into the other — noted in the file.

Compared to the old CLI's dev server, this drops the Python traceback filtering and stderr ring buffer. Raw output first; filtering can come back if it proves painful in practice.

Testing

Runner tests cover the missing-code-directory error, venv bootstrap vs. skip, the uvicorn/tsx command shapes, and env injection. Process tests cover line streaming, stderr classification, stop(), and a nonexistent binary. 565 tests pass, tsc clean.

Stack

#1880 (project foundation) → this PR → container runner → OTLP collector → Inspector web server → project dev handler.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 81.46067% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.75%. Comparing base (252c61c) to head (be40e1d).

Files with missing lines	Patch %	Lines
src/core/dev/run.ts	10.71%	25 Missing ⚠️
src/errors/errors.tsx	58.82%	7 Missing ⚠️
src/core/dev/process.ts	98.46%	1 Missing ⚠️

Additional details and impacted files

@@                     Coverage Diff                     @@
##           feat/project-foundation    #1883      +/-   ##
===========================================================
- Coverage                    96.01%   95.75%   -0.27%     
===========================================================
  Files                          208      211       +3     
  Lines                         9764     9942     +178     
===========================================================
+ Hits                          9375     9520     +145     
- Misses                         389      422      +33     

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