fix(dev-harness): resolve canonical Python venv

[Git-on-my-level]

Summary

• Centralize local dev-harness interpreter resolution: explicit PYTHON, then backend/.venv/bin/python, legacy backend/venv/bin/python, then python3.
• Route all harness commands and Makefile harness Python targets through the resolver; dev-init creates the canonical .venv when neither venv exists.
• Add focused resolver coverage for precedence and fallback behavior.

Root cause and durable guard

Harness commands and Makefile targets had inconsistent hard-coded legacy backend/venv defaults. A single resolver owns precedence now, with a hermetic regression test covering every selection branch.

Verification

• /Users/dazheng/workspace/omi/backend/.venv/bin/python -m pytest -q scripts/dev-harness/tests/test_python_resolver.py — 2 passed
• bash -n for the resolver plus all 9 harness consumers — pass
• git diff --cached --check — pass
• make preflight — passed (9 deterministic checks)

Failure-Class

Failure-Class: none

[chatgpt-codex-connector]

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[Git-on-my-level]

Monitor summary — Codex P2 "Preserve shell quoting for resolved Python"

Addressed by the existing head commit 74c62e05 (fix(dev-harness): quote resolved Python commands):

• Makefile now invokes the resolved interpreter as "$(PYTHON)" in list-memory-scenarios, seed-memory-scenario, reset-memory-scenario, and run-canonical-promotion, so checkouts whose absolute repo path contains spaces no longer split the venv path.
• Added regression test test_make_harness_targets_run_resolved_python_from_checkout_with_spaces exercising all four targets from a checkout path containing spaces.

Verification (in the monitor worktree, rebased onto origin/main c55f2925):

• git diff --check origin/main..HEAD — clean.
• bash -n on _resolve_python.sh and all 9 harness consumers — pass.
• python3 -m pytest -q scripts/dev-harness/tests/test_python_resolver.py — 3 passed.
• GitHub CI on the PR head: all checks terminal (SUCCESS/SKIPPED), none failing.

Thread PRRT_kwDOLkKqys6SDeWW resolved as addressed. No merge performed (still REVIEW_REQUIRED).

[kodjima33]

Dev-harness venv resolution fix. Approve-only (tooling).