TDS v3.5.3-dev6 — Guaranteed Storage Transition Fit

STATUS
- Opt-in bridge implemented; stable TDSPersistence default remains unchanged.
- Complete legacy-compatible mount images commit through one immutable generation.
- Bounded streaming image format with per-file SHA-256 validation.
- Atomic materialisation into a previously absent destination.
- Traversal, symlink, truncation, trailing-data, mutable-stream, and existing-target failures fail closed.

TEST EVIDENCE
- Transition + persistence focused qualification: 62 passed.
- Final critical transition/recovery recheck: 34 passed.
- Complete monolithic suite: 758 passed, 11 skipped, 0 failed in 81.67 seconds.
- Source hygiene: PASS.

RELEASE POSITION
- Development transition API only.
- No default persistence-path switch.
- Next work should qualify compound materialisation faults and then design incremental immutable segments to remove the bridge's duplicate-write cost without changing recovery semantics.
