perf(read): defer proven blob leaves during pack planning

[forhappy]

Summary

Avoid reconstructing proven blob leaves during shared upload-pack graph selection. The original planner fails the new minimized regression with a 2 MiB blob under a 64 KiB aggregate inflation budget. The retained Kubernetes depth-100 failure motivated this work, but its cold differential rerun is still pending.

• Admit visibility before using authenticated, pinned locator kind proof.
• Defer only non-root blobs under size-independent filters; preserve per-visit logical-object accounting, selection order, and deduplication.
• Keep bounded content reads for explicit roots, missing kind proof, and size-dependent filters.
• Preserve packed-entry verification, response limits, cancellation, and native Git installation checks. No budget increases, storage-format changes, or new configuration.

Ownership and scope

The change belongs in crab-read::plan_with_operation, shared by classic capsule fetch, upload-pack wire handling, and HTTP Git reads. Existing OperationContext::pinned_object_metadata provides snapshot-bound kind proof; it does not charge logical objects, so deferred visits are charged explicitly. Response generation remains responsible for packed-entry validation.

The regression publishes through the real capsule push path to an in-memory object store, plans a shallow response, installs its pack with native Git, verifies byte-identical blob content, and confirms explicit blob roots still hit the unchanged inflation limit. README documents the boundary.

Validation

• Original source: new regression fails with the expected inflated-byte limit error.
• Candidate: regression passes; 6 adjacent classic capsule tests and 30 shared planner tests pass (37 total).
• cargo fmt --all --check and git diff --check pass.
• cargo clippy --locked -p crab-read --all-targets -- -D warnings passes.

Container CI repair

The HTTP server image build failed before Rust compilation because Debian no longer publishes the pinned libpcre2-8-0=10.42-1+deb12u1 in the configured Bookworm repositories. With explicit user approval, both the server and Compose-example Dockerfiles now pin 10.42-1+deb12u2; image digests and security gates remain unchanged.

On the exact pinned Debian base, AMD64 (server package set) and ARM64 (Compose-example package set) both reproduced the obsolete-pin failure and installed the new exact version successfully. This is package-installation proof, not a full image/Compose qualification pass; current-head CI must supply that proof.

Still open

Draft pending current-candidate cold Kubernetes depth-100 verification, final exact-byte/integrity proof, and CI. This is not a claim that all shallow-clone amplification is eliminated. It does not waive push/fetch latency gates, establish matched-v1 performance, complete Xet/provider/recovery qualification, or retire v1. PR #208 is already merged; this is a follow-up against crab-v2.