feat(memory): KV cache preallocates its ring in Scope.Model (SKEEP-003 P2, S1.10)

[michalharakal]

Summary

SKEEP-003 slice S1.10 (milestone M1 #1002, PRD M1-F2): the KV cache preallocates its ring in Scope.Model.

The cache already preallocated the whole ring at construction — what it lacked was an owner. DefaultKvCacheStore now takes an optional ModelScope and allocates the per-layer K/V backing through it:

• tracked and traced — one Allocation event per layer and side, in MODEL scope, carrying the cache's TensorId (kv.layers[3].k / .v) rather than an anonymous buffer, so the ring shows up in plan-vs-actual (feat(memory): plan-vs-actual — reconstruct a run's memory from the event stream and fail on drift (SKEEP-003 P2, S1.9) #1074) as model-scope bytes and never as forward-scope churn;
• released deterministically when the model closes (Free events summing exactly to the ring size), instead of waiting for the GC — the Model.load(...).use { } story of §8 item 2;
• preallocatedBytes exposes what the ring costs (layers × 2 × heads × maxSeqLen × headDim × 4), so a caller can compare it with the plan's KV line directly.

Without a scope the store behaves exactly as before (plain arrays, GC lifetime), so nothing existing changes. The TurboQuant store keeps its block-encoded path; giving it the same owner is a follow-up.

Evidence (KvCacheModelScopeTest, 177/177 storage tests): the no-scope path is unchanged; with a scope the ring is allocated once per layer/side in MODEL scope with the right ids and total; appending tokens allocates nothing more; closing the model frees exactly the ring; and ActualMemory sees it as model-scope peak with zero forward bytes — the weights-vs-activations separation #1065 exists to enforce.

Test plan

Full local gate (scripts/pr-gate.sh, JDK 25) — all legs passed; results in the first comment.

Closes #1031

🤖 Generated with Claude Code

[michalharakal]

Local gate scripts/pr-gate.sh (JDK 25) on 4cf5096a: all legs passed — jvmTest · apiCheck · JS/Wasm · linuxX64Test · assemble · Java consumer API tests.

Targeted: sk.ainet.lang.tensor.storage.* 177/177.

[github-actions]

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