fix(checkpoint): guard _touch_project against non-dict project metadata

[wesleysimplicio]

Problem

tools.checkpoint_manager._touch_project parses the project metadata file with json.loads, then immediately subscript-assigns into the result:

try:
    meta = json.loads(meta_path.read_text(encoding="utf-8"))
except (OSError, ValueError):
    meta = {}
meta["workdir"] = str(_normalize_path(working_dir))  # ← crashes if meta is a list

When the file parses successfully but returns a non-dict ([], null, 42, etc. — from a corrupted or truncated write), json.loads does not raise, the except (OSError, ValueError) clause is skipped, and meta["workdir"] = ... raises TypeError: list indices must be integers or slices, not str.

This TypeError is not caught in _touch_project or _take. It propagates to ensure_checkpoint's broad except Exception safety net, which silently returns False — disabling all checkpoints for the affected working directory for the entire session, with no user-visible error.

Root cause

Missing isinstance(meta, dict) guard after json.loads. The same guard is already present in _list_projects (line 506 of the same file) but was omitted in _touch_project. Same pattern as fixes in cron/jobs.py (#22569) and tools/process_registry.py (#22544).

Fix

     try:
         meta = json.loads(meta_path.read_text(encoding="utf-8"))
     except (OSError, ValueError):
         meta = {}
+    if not isinstance(meta, dict):
+        meta = {}
     meta["workdir"] = str(_normalize_path(working_dir))

Two lines, matching the existing guard in _list_projects.

Tests

TestTouchProjectMalformedMeta covers four non-dict payloads ([], null, 42, "oops"):

• Writes corrupted metadata to <store>/projects/<hash>.json
• Calls _touch_project — asserts no exception raised
• Asserts metadata file is rewritten as a valid dict with last_touch and workdir present

All four cases fail on main with TypeError, pass with the fix. Full tests/tools/test_checkpoint_manager.py regression: 77 passed.

[Copilot]

Pull request overview

This PR hardens tools.checkpoint_manager._touch_project against corrupted-but-JSON-valid project metadata by ensuring the parsed metadata is a dict before performing key assignments, preventing a TypeError that could silently disable checkpointing for a session.

Changes:

• Add a post-json.loads shape guard in _touch_project to coerce non-dict payloads to {}.
• Add a regression test suite covering several non-dict JSON payloads and asserting _touch_project repairs the metadata file.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tools/checkpoint_manager.py	Adds isinstance(meta, dict) guard to prevent TypeError when metadata JSON root is not an object.
tests/tools/test_checkpoint_manager.py	Adds parametrized regression tests for malformed metadata shapes to ensure _touch_project does not raise and rewrites valid metadata.

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[teknium1]

Merged via salvage PR #22848. salvage cherry-picked your commit; authorship preserved. Thanks for the contribution!