feat(v3): add BinShim substrate carrier

[briansrls]

Summary

• add staged v3 std authority for the BinShim carrier with the locked fields entrypoint_name, description, and entry
• keep entry as DeclarationRef per docs/design-pb-runtime-interpreter.md §4.2/§5.4; no PipelineStep DSL, emitter, runtime behavior, or PB-owned instance rows in this slice
• add a focused integration carrier-shape ratchet for authority location, field order, and field target types
• refresh bootstrap generated snapshots

Validation

• cargo run -p v3-compiler --features bootstrap-regen-fresh --bin regen_bootstrap
• CARGO_INCREMENTAL=0 cargo run -p v3-compiler --features bootstrap-regen-fresh --bin regen_bootstrap -- --verify
• cargo fmt --all --check
• git diff --check HEAD~1 HEAD

Local limitation

• CARGO_INCREMENTAL=0 cargo test -p v3-compiler --test integration bin_shim_carrier_test -- --nocapture was attempted twice, but local compilation did not reach test execution after ~30 minutes due sccache fallback/local rustc slowness; no test failure was emitted.

[briansrls]

Review metadata

• Provider / model: cursor / composer-2
• Commit: f7ad3b94 · Trigger: schedule
• Comparison: origin/main @ 0994d763 ... review/pr-1361-f7ad3b94 @ f7ad3b94
• Thinking: 104s wall

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Findings

• None. The diff adds a small substrate carrier (src/v3/std/bin_shim.dag), regenerates the two bootstrap snapshots, and wires a carrier-shape ratchet test. Coproduct classification is explicitly 🟢 with an in-diff rationale, and the temporary looseness of entry: DeclarationRef is called out with a forward typing trigger (src/v3/std/bin_shim.dag lines 15–17), which matches the modeling-discipline scaffold/terminal guidance rather than silent ambiguity.

Verdict

APPROVE — Scope matches the locked PB-Runtime bin-shim story (authority cited in-module; PB-owned instances deferred). Bootstrap plus integration ratchet tests mirror existing carrier tests (e.g. bridge_ledger_carrier_test.rs), and nothing here duplicates a second authority for the carrier shape or violates fail-closed / boundary discipline in a way visible in the diff.

Exploratory (optional)

• Locked prose elsewhere mentions paths like dsl/std/runtime/bin_shim.dag; this PR correctly lands the type under src/v3/std/ and documents that split in comments and tests (bin_shim_carrier_test.rs lines 39–42). If reviewers care about doc–path parity, a doc-only alignment later might reduce confusion; it is not a diff violation.
• bin_shim_carrier_has_locked_three_field_shape asserts label order (bin_shim_carrier_test.rs lines 54–56). If declaration field order is not part of the public contract, a set-based check (like some bridge_ledger tests) could be slightly less brittle; if order is reflection-relevant, the current form is fine.

[briansrls]

Review metadata

• Provider / model: cursor / composer-2
• Commit: 2852e83a · Trigger: schedule
• Comparison: origin/main @ 0994d763 ... review/pr-1361-2852e83a @ 2852e83a
• Thinking: 119s wall

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Reviewed git diff origin/main...HEAD (5 files: new src/v3/std/bin_shim.dag, new bin_shim_carrier_test.rs, integration.rs wiring, and regenerated bootstrap_generated*.rs churn from the new declaration).

Findings: None. Nothing in the diff clearly breaks INVARIANTS, docs/modeling-discipline.md, CODING.md, or TESTING.md.

• P1 / modeling: BinShim is a single record carrier with authority split called out in-file (src/v3/std/bin_shim.dag:4-6), entry left as DeclarationRef with an explicit forward note until signature refinement (src/v3/std/bin_shim.dag:15-17), and a 🟢 terminal rationale tied to the locked design doc (src/v3/std/bin_shim.dag:13-18).
• P2: One substrate type for the shape; instance rows stay PB-owned elsewhere — no second authority in this diff.
• Tests: Integration ratchet on declared carrier shape and file authority (src/v3/compiler/tests/integration/bin_shim_carrier_test.rs:33-78) matches the “cementing / structural substrate” style TESTING.md allows; names are behavior-shaped.

Verdict: APPROVE — Small, scoped carrier plus bootstrap regen and a focused shape ratchet; no rubric violations identified in the diff.