Seal Git substrate out of v19 receipts, ticks, and evidence

[flyingrobots]

Parent: #734

Blocked by: #735

Outcome

The v19 root API speaks only in Timeline, Intent, Reading, Tick, Receipt, Evidence, and opaque storage handles. Git commits, refs, SHAs, OIDs, trees, blobs, plumbing, and git-cas implementation handles are absent from the root declaration graph and normal control flow.

Scope

• Replace StorageAdapter = CorePersistence with the opaque storage handle established by Adopt git-cas v6.2 as the sole storage composition root #735.
• Replace WriteReceipt.patchSha and JoinReceipt.patchShas with resulting Tick/evidence handles.
• Replace Git-shaped ReadEvidence fields with storage-neutral causal basis and support handles.
• Make serialized Tick identity opaque and storage-neutral.
• Keep raw Git and git-cas provenance available only through the diagnostics subpath.
• Add a transitive emitted-declaration vocabulary gate, not merely an export-name gate.

Proof

• The root .d.ts reachability graph contains no public sha, oid, ref, commit, blob, tree, or plumbing fields or dependencies.
• First-use write, read, join, historical-read, and receipt examples contain no Git vocabulary.
• Diagnostics can still recover exact substrate evidence from a receipt with explicit storage context.
• Existing causal identity, deterministic join, and bounded-read behavior remains unchanged.

[flyingrobots]

This slice was added after the v19 public API audit found that export-name pruning did not remove transitively reachable Git-shaped fields. It follows #735 so the diagnostics resolver can target the final opaque storage boundary.

[coderabbitai]

🔗 Related PRs

#93 - Fix recursive tree OID read fanout and release v17.0.1 [merged]
#726 - Move graph exports behind v19 public API boundary [merged]
#729 - Add v19 timeline intents, readings, and drafts [merged]
#732 - Fix: anchor state-cache payloads against Git GC [merged]
#733 - Enforce the v19 public API contract [merged]

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