fix: resolve native Codex CLI on Windows PATH (#70)

[James3014]

Summary

Fixes #70 — resolves native Codex CLI binary discovery on Windows by using the correct platform path delimiter and searching for codex.exe instead of codex.

Root cause

resolveCodexBinary() used path.delimiter from a POSIX-biased import and searched only for codex (without .exe), causing complete PATH lookup failure on Windows even when Codex is correctly installed.

Changes

src/codex-goal-sessions.ts — resolveCodexBinary():

• Import posix and win32 from node:path instead of delimiter
• Use win32.delimiter on Windows, posix.delimiter on POSIX
• Search codex.exe on Windows, codex on POSIX

src/codex-goal-sessions.test.ts — new test suite:

• Hostile controls for win32 and platform contracts
• Verifies correct delimiter and candidate name selection per platform
• Maintains pre-existing override/PATH/fail-clearly contract

Verification evidence

• 2/2 focused resolver tests PASS
• 97/97 CI tests PASS (codex-goal-sessions-ci.test.ts)
• Build: ✓ built in 881ms
• git diff --check: clean
• Blob SHAs:
  • src/codex-goal-sessions.ts: d79abab34ddc122162a09ab78bccf513f5ebf713
  • src/codex-goal-sessions.test.ts: 65f87c6f1b233ad1fa092592b55f7861f0e55a23

Candidate

• HEAD: e4bad89e6d525bce8b116d5fc76177fd28432306
• Parent: 5db22fd8a642016ad8a7a4fdbcd31e56d345a707 (current main)
• Changed paths exactly: src/codex-goal-sessions.ts, src/codex-goal-sessions.test.ts

Outstanding

• Real Windows runtime probe pending (no Windows host available in macOS CI environment)

Claim ceiling: ISSUE_70_SOURCE_CANDIDATE_LOCAL_VERIFIED_PENDING_REMOTE_CI_AND_INDEPENDENT_ACCEPTANCE

[James3014]

Superseded by codex/issue-70-windows-codex-exe-final-r2 bound to fresh main ee47c11 with splitPathEnv Windows colon repair.