Adopt git-cas v6.2 as the sole storage composition root

[flyingrobots]

Parent: #734

Prerequisite complete: git-stunts/git-cas#60 shipped in @git-stunts/git-cas@6.2.0 and is visible on npm.

Outcome

Applications open one opaque repository-scoped GitStorage handle. Internally, the composition root owns sibling Git-history and git-cas adapters; neither the public API nor the domain layer receives plumbing, concrete adapters, or raw CAS construction capabilities.

Scope

• Add GitStorage.open({ cwd }) and MemoryStorage.create() as the supported storage constructors.
• Replace the public Git-shaped StorageAdapter contract with an opaque WarpStorage handle.
• Compose GitTimelineHistoryAdapter and GitCasRepositoryAdapter as siblings under GitStorage.
• Open and inject exactly one repository-scoped git-cas facade.
• Remove dynamic CAS construction and reflected runtime adapter construction.
• Keep Git history semantics separate from git-cas asset/cache/retention semantics.
• Remove duplicate lazy CAS initializers and WARP-owned encryption validation already enforced by git-cas.
• Expose domain capabilities as semantic WARP storage services, not raw object ports.

Proof

• The first-use Git quick start imports neither @git-stunts/plumbing nor @git-stunts/git-cas.
• Runtime construction works through GitStorage and MemoryStorage.
• One GitStorage instance shares one git-cas facade across all CAS-backed services.
• No domain module imports concrete storage adapters, @git-stunts/plumbing, or @git-stunts/git-cas.
• Existing timeline, patch, checkpoint, trust, and content smoke tests pass.
• Related composition leaks runtimeHelpers imports infrastructure adapters and branches on plumbing presence #174 and WarpRuntime.open constructs infrastructure adapters by peeking at plumbing #182 are closed with source evidence or explicitly narrowed.

Receipt, Tick, and Evidence substrate vocabulary is tracked separately by #743.

[coderabbitai]

🔗 Related PRs

#24 - feat: InMemoryGraphAdapter (MEM-ADAPTER, v10.7.0) [merged]
#93 - Fix recursive tree OID read fanout and release v17.0.1 [merged]
#726 - Move graph exports behind v19 public API boundary [merged]
#727 - Expose diagnostics materialization scope helpers [merged]
#728 - Add openWarp timeline facade [merged]

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