v5.5.0 — V5-3 storage cutover: device-local is canonical

MINOR. The kernel no longer contains a built-in vault backend. State (harness_state_dir, read_state_file, write_state_file) is device-local only; phase_recall returns ""; resolve_documenter_context returns None. The vault is reachable only through the obsidian-vault plugin; a config-file storage.backend=vault with no vault accessible now raises StorageBackendNotInstalledError — never a silent demotion to device-local. Four locked design calls in ADR 0018. Gates: 20/20, CI green across Linux/Mac/Windows.

What shipped

• V5-3 — lock A2 index invariant (53f96fa). scripts/test_a2_index_invariant.py — gate confirming vector index stays under ~/.cache/agentm/, never inside the synced vault root.
• V5-3 — vault-root rename tooling (cd78cdd, 1358e1d). scripts/rename-vault-root.sh — Phase A backup+runbook, Phase B string sweep across 36 files. Used to execute the AgentMemory → Agent rename.
• V5-3 — group rename: personal-private → personal (053217b). 3-part lockstep: kernel _ALWAYS_LOAD_REL, plugin vault_probe.py, 10 skill scripts.
• V5-3 — delete vault backend from kernel; device-local state only (8cb2b48). harness_memory.py — harness_state_dir/read_state_file/write_state_file unconditional device-local; phase_recall → ""; resolve_documenter_context → None.
• V5-3 — vault_path() fail-loud guard (05e63d3). StorageBackendNotInstalledError raised when storage.backend=vault configured but no vault accessible. $MEMORY_VAULT_PATH env override remains graceful-skip. Six tests in TestVaultPathGuard.
• V5-3 — ADR 0018; HLD v0.9; ADR 0010/0013 amendments (8ce8824). Seven V5-3 design calls documented. ADR 0010 re-audit trigger #1 closed. ADR 0013 negative bullets resolved.

See also

• ADR 0018 — full design record.
• Completed Features — V5-3 — narrative summary.