Saving a session fails when the state root is a junction on Windows #7098

Saving a session fails outright on Windows when the Codewhale state root is
relocated to another volume — the supported way to keep ~/.codewhale off the
system drive. Nothing is written, no conversation is kept, and the only signal
is a red "cannot save session" notice.

Environment

• Codewhale 0.10.2 (release binary, codewhale 0.10.2 (ff466b2ed0bf))

• Windows 11, %USERPROFILE%\.codewhale is a directory junction:

  mklink /J C:\Users\<user>\.codewhale D:\CodeWhaleData
  

• Same behaviour with any volume the state root is relocated to.

Steps to reproduce

1. Relocate the state root with a directory junction as above.
2. Run any session that persists: codewhale exec --auto "Run: echo hello", or
   an interactive session's autosave / /save.
3. Observe the red "cannot save session" notice, and the log.

Expected

The session document is written under the junction target
(sessions/<id>.json), as it is on a non-relocated install.

Actual

No session document is written. logs/tui-*.log records one line per attempt:

WARN persistence: persistence write failed what=session:<id>
  error_kind=InvalidInput
  error=Fleet artifact path must stay within the workspace

The failure is not in the write itself. SessionManager::save_session_inner
hydrates approval receipts before it serializes the document, and
ApprovalReceiptStore::log_file opens
<sessions>/<id>/approval_receipts.jsonl through the strictly confined
WorkspaceFile::open. On Windows that opener walks the path component by
component and refuses any reparse point — including the junction that is the
state root — so the save dies before reaching the write_atomic call that would
have written the document.

open_resolved_root exists for exactly this case (added in #6947; #6949 made
the same distinction for sub-agent state): it resolves the root once, then runs
the same link-refusing walk below it. The session-side state opens were never
converted to it.

Evidence

With the reported layout, the built binary from the fixing branch:

• codewhale exec --auto "Run the shell command: echo CWJUNCTION_OK" → exit 0,
  wrote sessions/cf02b940-8436-4289-b16b-756d7a516228.json (58,986 bytes)
  through the junction.
• The same layout on the 0.10.2 release binary produced the warning above and no
  document.

Same class of failure as #6947 (session artifacts) and #6949 (sub-agent state):
a user-owned relocated root treated as if it were an untrusted workspace root.

Attribution

🤖 Generated by SpikeBot 000(CodeWhale-LOCAL)