fix(tests,mcp): harden _run_cli helper + propagate exit codes under python -m

[Huntehhh]

Summary

Two tiny additive fixes that close the test-infrastructure gap left open by #351 (PR-2b Windows subprocess portability). Surfaced live by a test run on a hardened-Win11 Block-mode ASR host hitting Defender on truememory-ingest.exe.

Branched off origin/main directly. Different region from #351's edits in the same file — mechanical merge regardless of order.

What changed

tests/test_cli_help.py:_run_cli helper

Replaced the two-arm helper (shutil.which("truememory-mcp") → bare shim, fall back to python -m) with a single [sys.executable, "-m", "truememory.mcp_server"] invocation. The shim path is faster (cached imports) but is a setuptools / uv trampoline with a per-install unique hash — Microsoft Defender's Attack-Surface-Reduction rule 01443614-cd74-433a-b99e-2ecdc07bfc25 ("Block executable files from running unless they meet a prevalence, age, or trusted list criteria") silently kills it at launch on hardened Win11 baselines. Routing through the signed python.exe wrapper passes ASR everywhere; the per-test re-import cost is negligible at test scale.

truememory/mcp_server.py:1521 (__main__ block)

Changed main() to sys.exit(main() or 0). The setuptools console-script wrapper around truememory-mcp already does sys.exit(main()), so exit codes propagated correctly under the shim. Under python -m the bare main() discarded the return value — exit-code-2 paths (unknown flag, positional-arg typo) silently masked as exit 0.

Bundled here because the _run_cli rewrite above exposed the bug: 2 of the 7 newly -m-routed tests assert returncode != 0 (test_unknown_flag_exits_nonzero_not_hang, test_positional_arg_exits_nonzero_not_hang). Without the sys.exit line, those would silently fail on every CI run that exercised python -m. Single-concern in spirit — "make python -m truememory.mcp_server behave like the shim under all invocation paths" — even though it touches two files.

Test results (Windows, Defender ASR Block mode)

Before this PR:

0 of 9 tests in test_cli_help.py pass
9 PermissionError [WinError 5] Access is denied (shim ASR-blocked)

After this PR:

7 of 9 tests pass
2 remaining failures: test_help_via_console_script_does_not_hang +
                     test_ingest_version_flag_exits_cleanly

The 2 remaining are PR-2b (#351) territory — they invoke the shim directly outside the helper at lines 94-98 + 137-152. Will pass once #351 lands (or when this branch rebases on it).

Test plan

• pytest tests/test_cli_help.py -v on Linux / macOS — all 9 pass (no ASR there)
• pytest tests/test_cli_help.py -v on Windows Block-mode ASR — 7 of 9 pass (until fix(mcp,model_server,hooks,ingest): Windows subprocess portability #351 merges, then 9 of 9)
• python -m truememory.mcp_server --halp — exits 2 with usage text on stderr (previously exited 0)
• python -m truememory.mcp_server help (positional, no dashes) — exits 2 (previously exited 0)
• truememory-mcp --halp via the shim — still exits 2 (unchanged behaviour)

Coordination context (multi-agent sweep)

PR-2c in the sweep registered after agent-B's PR-2b (#351) explicitly handed off the _run_cli-helper hardening (agent-B relay 2026-05-17 ~02:20 ET — "test-infra single-concern, doesn't belong on top of subprocess story").

Sibling sweep PRs:

• agent-A: #344 (cold-start) · #345 (fcntl) · #347 (engine + tier-switch)
• agent-B: #346 (installer ASR) · #351 (subprocess portability) · PR-2a CI runner pending
• agent-C: #348 (_setup_claude hygiene) · #349 (logging + Popen cleanup) · #350 (docs Windows callouts) · this PR

mcp_server.py:1521 is unclaimed by any other agent's file ownership region per the multi-agent coordination registry.

Merge ordering

Order-independent against #351. Different region of tests/test_cli_help.py from #351 (this PR rewrites the _run_cli helper at lines 19-36; #351 fixes the two shim-direct tests at lines 94-98 + 137-152). Mechanical inter-PR merge regardless of order.

Depends on: none. mcp_server.py:1521 (sys.exit(main() or 0) line in the __main__ block) is unclaimed by any other agent's file ownership region.

Blocks: none.

Recommended sequence position: after #344 / #345 / #351 so the test-helper fixes are validated against the full subprocess-portability stack on a Windows runner (#353).