fix(agent-replay): preserve guest path compatibility on Windows

[hugozhou-ai]

Summary

• keep replay CWD and portable state paths in the provider guest POSIX namespace on Windows hosts
• allow older Codex cassettes to match the newer turn/start.cwd field only when it equals the declared default replay CWD
• validate POSIX and Windows absolute paths independently of the host OS while preserving user-authored text

Why

Native Windows TSH replay runs execute the provider inside a Linux HCS guest. Host filepath semantics rejected or rewrote guest paths, while older Cassettes omitted the default Codex turn/start.cwd field now emitted by newer providers.

Risk

The compatibility rule is descriptor-owned and narrow: it applies only to declared methods, only when the recorded field is absent, and only when the live value exactly equals the replay CWD. Non-default CWD mismatches continue to fail closed.

Verification

• go test ./... in packages/agent/session-replay
• go test ./packages/agent/daemon/runtime -run 'TestReplayProcessTransport(AcceptsDefaultCWDAddedByNewerProvider|MapsRecordedCWDInStrictJSONMatch|FailsClosedOnOutboundMismatch)$' -count=1
• real TSH C01 replay completed 8/8 checkpoints twice with C01_TURN_3_COMPLETED
• git diff --check origin/main...HEAD

Windows impact

Covered by cross-platform absolute-path tests, logical POSIX replay-root tests, and the real native HCS/VMP replay runs above.

Documentation impact

No durable documentation change is required. The existing Session Replay README already defines ${REPLAY_CWD} as the portable guest-path boundary; this change makes Windows implementation match that contract.