fix(ce-work): probe ignored snapshot capability before dispatch

[nathanvale]

Summary

• Probe the canonical checkout's ignored inventory during prepare, before external authoring starts.
• Report every exact-snapshot blocker together: entry and byte excess, symlinks, non-regular entries, hardlinks, opaque directories, ownership mismatches, unsafe parents, and inspection failures.
• Keep the existing integrate-time preflight authoritative, so ignored-state changes after prepare still fail closed.
• Document the constraint and native-execution repair route in the cross-model contract.

This is a containment fix for #1300. It stops users paying for external authoring that cannot integrate; it does not change ignored snapshot semantics.

Motivation

The reported real checkout has 12,345 ignored entries: 12,100 regular files, 219 symlinks, 26 opaque directory entries, and about 623 MB of regular payload. The existing 512-entry / 64 MiB snapshot limits and unsupported entry representations only refuse after external authoring has completed.

Validation

• python3 -m py_compile skills/ce-work/scripts/unit_workspace_ignored.py skills/ce-work/scripts/unit_workspace_jobs.py skills/ce-work/scripts/unit_workspace_transaction.py
• bun test tests/skills/ce-work-unit-workspace.test.ts (85 passed)
• bun run test (2,871 passed)
• bun run release:validate

Fixtures use scratch Git repositories and cover entry cap, byte cap, symlink, multi-link file, ownership mismatch, opaque directory entry, and all-clear pass-through. I can also validate this branch against the measured 12.3k-entry checkout shape if useful.

Security Disclosure

Adds read-only filesystem metadata and ownership inspection before external dispatch. The probe uses the existing bounded Git ignored inventory and path-containment checks, performs no copy or mutation, and returns a bounded 10-entry offender sample. No dependency, credential, shell-execution, or permission changes.

Agent Disclosure

• Model: Codex · GPT-5

[chatgpt-codex-connector]

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[tmchow]

Nice fix @nathanvale