fix(agent): settle finalized SWM after catch-up

[branarakic]

User impact

A cold Edge receiver that explicitly subscribes to a public Context Graph now converges to one user-visible finalized state after foreground catch-up:

• finalized content remains visible in Verifiable Memory;
• the publisher's physically retained SWM recovery copy is hidden from the user-facing SWM view;
• a newer or unmatched SWM draft remains visible;
• no global subscription or all-CG synchronization is introduced.

This closes the testnet-canary seam where durable VM catch-up succeeded first, then public SWM snapshot materialization re-exposed the same finalized assertion as live SWM.

Before

sequenceDiagram
    participant E as Cold Edge
    participant C as Core provider
    participant S as Local store
    participant Q as User query

    E->>C: Foreground durable VM catch-up
    C-->>E: Finalized assertion and confirmed metadata
    E->>S: Store exact VM
    E->>C: Public SWM snapshot catch-up
    C-->>E: Retained recovery snapshot and verified head
    E->>S: Materialize SWM and advance checkpoint
    Q->>S: Query VM and SWM
    S-->>Q: Finalized assertion appears in both views

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After

sequenceDiagram
    participant E as Cold Edge
    participant C as Core provider
    participant B as Chain
    participant S as Local store
    participant Q as User query

    E->>C: Foreground durable VM catch-up
    C-->>E: Finalized assertion and confirmed metadata
    E->>S: Store exact VM
    E->>C: Public SWM snapshot catch-up
    C-->>E: Retained recovery snapshot and verified head
    E->>S: Materialize SWM and verified metadata
    E->>S: Reverify exact confirmed VM
    E->>B: Read latest root, version, and CG binding
    B-->>E: Current canonical state
    E->>S: Recheck exact SWM under per-KA writer lock
    E->>S: Stamp local retirement marker
    E->>E: Advance sync checkpoint
    Q->>S: Query VM and SWM
    S-->>Q: Finalized assertion only in VM; newer SWM drafts remain

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Safety properties

• Peer metadata alone cannot retire SWM. The receiver requires surviving confirmed VM metadata and exact local VM content.
• Root, assertion version, KA-to-CG binding, and local CG identity are re-read from chain while the shared per-KA writer lock is held.
• The exact current SWM head is re-read and verified under that lock before the marker is written.
• The physical SWM snapshot is retained for recovery or reorg handling.
• If chain verification or the retirement handoff fails, meta/data checkpoints do not advance and the sync remains retryable/incomplete.
• Unfinalized drafts and superseded snapshots are not retired.

Validation

• Focused finalization and SWM materialization lane: 62 passed.
• Full Agent unit lane: 165 files, 2,241 passed, 5 skipped, 0 failed.
• Agent build: TypeScript, type-contract tests, and package-root test passed.
• git diff --check passed.

Stack

Stacked on #2034. The fresh two-node testnet-canary validation runs against this exact head after review CI starts; no production Core deployment and no merge are part of this PR.