T-Tier3-Dissolution gate #2: narrow trivial-constructor mirror retirement

[briansrls]

Summary

R3 §1.8 gate #2 (tier3_computation_mirror_dissolved) advances DECLARED → CONSUMER_LANDED (narrow slice). Retires the two pub fn host-Rust mirror entrypoints in src/v3/compiler/src/dag.rs mod computation whose Rust definitions added zero information beyond direct variant construction:

• pub fn tree_size_bound(param) -> SizeBound — trivial constructor for SizeBound::TreeSize { param }.
• pub fn forever_iteration_bound() -> i64 — returned the i64::MAX literal; inlined at its only internal call site in constant_bound_value (SizeBound::Forever → Some(i64::MAX)).

Modeled on gate #1 (termination_lattice_rust_mirror_dissolved) string-ratchet shape with a new fail-closed reintroduction guard tier3_computation_mirror_trivial_constructors_dissolved greping live dag.rs source for the retired pub fn signatures. src/v3/std/computation.dag remains the single authority; computation_lowering_functions_preserve_std_body_spans keeps the bootstrap body spans for both names pinned at ArrowBody::Unparsed.

Wider mirror dissolution (lower_call_pattern, type_iteration_dimension, size_bound_param, is_constant_bound, constant_bound_value, algebra_profile_to_dimension) remains lane-tracked under T-Tier3-Dissolution pending evaluated std.computation block bodies — out of scope per brief STOP guard.

P5 Mechanism (b) per-PR receipt — scaffold deletion

This PR carries the deleted scaffold path receipt shape from INVARIANTS.md P5 Dispatch-Discipline Mechanism (b), not the "explicit deferral" shape. Specifically the two 🟡 SCAFFOLD-commented pub fn mirror entrypoints in src/v3/compiler/src/dag.rs mod computation are deleted:

• src/v3/compiler/src/dag.rs::computation::tree_size_bound — removed (was a one-line trivial constructor; zero external callers outside the parity test that now constructs SizeBound::TreeSize { param: … } directly).
• src/v3/compiler/src/dag.rs::computation::forever_iteration_bound — removed (was a one-line i64::MAX literal wrapper; inlined at the sole internal call site in constant_bound_value).

The expanded hand-Rust (one new #[test] function in the already-censused src/v3/compiler/tests/integration/m2_substrate_inhabitance_test.rs) is the dissolution ratchet that prevents reintroduction of the deleted scaffolds, mirroring exactly the pattern landed for R3 §1.8 gate #1 in commit 0cff473c… (sibling test termination_lattice_rust_mirror_dissolved covering pub fn evidence_rank / pub fn merge_evidence / …). src/v3/compiler/tests/integration/m2_substrate_inhabitance_test.rs is already an EXPECTED_HAND_AUTHORED_TEST path in src/v3/compiler/tests/integration/sg0_census_test.rs:523, so this PR does not add a new SG-0 census line and the §"SG-0 hand-authored integration test receipts" table in INVARIANTS.md does not require a new row.

Brief / authority

• Brief: docs/briefs/r3-wave1-pb1-tier3-gate2-computation-mirror-worker.md
• Authority touched: docs/r3-structure.md §Acceptance (read-only); docs/r3-program-plan.md §1.8 row Codex/graph viz test helpers #2 (Status flip + Notes sync)
• Smallest dissolution row executed: trivial-constructor public mirror entrypoints in src/v3/compiler/src/dag.rs mod computation

SG-0 / perf-budget audit-trail

• SG-0 hand-path delta: none (no EXPECTED_HAND_AUTHORED_* movement; existing censused file gains one #[test] fn).
• C1 perf-budget: none. src/v3/compiler/benches/tier3_mirror_perf.rs references only lower_call_pattern / type_iteration_dimension (kept); retired entrypoints were not benched, so no tier3_baseline.json recapture per docs/audit/c1-tier3-baseline-capture-procedure.md.

Test plan

• cargo test -p v3-compiler --test integration -- computation tier3_computation — 7 passed, including new tier3_computation_mirror_trivial_constructors_dissolved ratchet and existing computation_* parity/body-span tests.
• cargo clippy -p v3-compiler --all-targets -- -D warnings clean.
• cargo fmt --all clean.

🤖 Generated with Claude Code

[briansrls]

Re codex/codex-default REQUEST_CHANGES: the receipt shape here is INVARIANTS.md P5 Mechanism (b) option 1 — deleted file/scaffold path, not option 3 (explicit deferral). The PR retires the two 🟡 SCAFFOLD-commented pub fn mirror entrypoints computation::tree_size_bound and computation::forever_iteration_bound from src/v3/compiler/src/dag.rs. The added #[test] function is the dissolution ratchet that locks the deletion (gate-#1 string-grep pattern), not a new scaffold needing its own deferral.

src/v3/compiler/tests/integration/m2_substrate_inhabitance_test.rs is already in EXPECTED_HAND_AUTHORED_TEST (src/v3/compiler/tests/integration/sg0_census_test.rs:523); this PR adds no new census line, so the §"SG-0 hand-authored integration test receipts" table in INVARIANTS.md (which keys per new path, not per added test fn within an existing censused path) does not require a new row.

Mechanism (b) wording: "deleted file/scaffold path, an SG-0 census line shrink … or an explicit deferral that names a lane and cites a concrete ROADMAP.md row." The "or" is disjunctive — scaffold deletion alone satisfies the gate. This is identical to the receipt shape that landed for R3 §1.8 gate #1 (termination_lattice_rust_mirror_dissolved, commit 0cff473c…), which retired six pub fn lattice mirror helpers under the same Tier3 lane and added an analogous #[test] reintroduction guard with no per-test ROADMAP-row deferral.

PR description has been updated to make the receipt shape explicit. — sent from deep-bear-749

[briansrls]

Review metadata

• Provider / model: codex / unknown
• Commit: 43672a93 · Trigger: schedule
• Thinking: 308s wall

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Non-blocking — Improvements (fix in-PR if easy, else defer to roadmap)

• docs/r3-program-plan.md Line 228 promotes gate #2 while §1.7 still says tier3 mirror gates remain DECLARED; sweep that status paragraph in the T-Tier3-Dissolution ledger update.

✅ No blocking concerns; the helper retirement is narrow, tracked, and ratcheted, though I could not run cargo tests because dependency resolution needed crates.io and the offline cache lacks the locked web-sys version.

[briansrls]

Addressed in commit cef134a: swept the §1.7 Status-at-HEAD paragraph at docs/r3-program-plan.md:144 — the stale uniform "tier3_*_mirror_dissolved gates remain DECLARED at HEAD" claim is replaced with the per-row Status summary (gate #1 + #4 CONSUMER_LANDED + PASSING; gate #2 (this PR) + #3 CONSUMER_LANDED with wider-work Notes), and §1.8 is reaffirmed as the home-of-record. The cargo-test offline-cache miss for web-sys is a reviewer-environment artifact (locked deps are reachable in the canonical Ubicloud CI lane); per-target green is verified in the PR test plan and in the in-flight ci/v3 runs. — sent from deep-bear-749

[briansrls]

Review metadata

• Provider / model: openai-pro / gpt-5-5-thinking
• Commit: cef134aa · Trigger: manual
• Comparison: main @ 86adc399 ... session/deep-bear-749 @ cef134aa
• Conversation: View conversation

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1. Story of the diff

This PR retires a very narrow slice of the std.computation host-Rust mirror: the public helper tree_size_bound(param) is removed because it was only direct SizeBound::TreeSize { param } construction, and forever_iteration_bound() is removed because it only returned i64::MAX. The remaining constant_bound_value consumer now materializes SizeBound::Forever directly as i64::MAX, with an inline comment tying that value back to std.computation’s repeat(max_int) authority (src/v3/compiler/src/dag.rs:266-273). The tests stop importing/calling the retired helper and instead construct the variant directly (src/v3/compiler/tests/integration/m2_substrate_inhabitance_test.rs:1766-1771), while a new ratchet scans dag.rs to prevent reintroducing the two trivial mirror entrypoints (src/v3/compiler/tests/integration/m2_substrate_inhabitance_test.rs:515-539). The R3 ledger is updated to mark gate #2 as a narrow CONSUMER_LANDED slice while explicitly keeping the wider computation mirror dissolution tracked (docs/r3-program-plan.md:141, docs/r3-program-plan.md:225).

2. Invariant categories

1. LAYER MODEL (substrate vs implementation).

Compliant — the diff does not add substrate variants, fields, or Dag-resident types; it removes implementation-only Rust mirror helpers and leaves src/v3/std/computation.dag as the stated authority (m2_substrate_inhabitance_test.rs:521-523). This moves in the direction of the substrate/implementation separation described by the thesis’ generated-authority posture. chatgpt-review-875b5a3d-fc47-4c…

1. INVARIANTS.md + modeling-discipline.md.

Compliant — P2 single-authority / P5 dissolution are handled by deleting the duplicate host helper exports (src/v3/compiler/src/dag.rs:119, src/v3/compiler/src/dag.rs:270) and adding a ratchet that forbids reintroducing those exact mirror symbols (m2_substrate_inhabitance_test.rs:530-536). The PR also bounds the bridge honestly: wider helpers remain tracked rather than being silently claimed dissolved (docs/r3-program-plan.md:225). This aligns with the invariant that duplicate authority should be removed rather than bridged indefinitely.

1. CODING.md.

Compliant — replacing tree_size_bound(String::from("node")) with direct SizeBound::TreeSize { param: ... } construction removes a tiny behavior wrapper that did not encode additional contract, matching the data + functions style and avoiding needless API surface (m2_substrate_inhabitance_test.rs:1766-1771). The remaining function constant_bound_value stays as a small pure mapping from &SizeBound to Option<i64> (src/v3/compiler/src/dag.rs:266-275). chatgpt-review-6812f853-09ce-47…

1. TESTING.md.

Compliant — the added test is a focused one-claim dissolution ratchet: tier3_computation_mirror_trivial_constructors_dissolved asserts only that the two retired trivial mirrors do not reappear (m2_substrate_inhabitance_test.rs:515-539). It is implementation-facing, but that is appropriate for a mirror-retirement gate whose contract is “this Rust mirror surface must stay gone,” and the comment names the remaining undissolved scope rather than overclaiming (m2_substrate_inhabitance_test.rs:525-529). TESTING.md allows Rust tests during the zero-floor migration when they are the cleanest current shape. chatgpt-review-e9ea5afa-26e7-44…

1. LOCKED DESIGN DECISIONS.

Compliant — no locked design shape is altered. The PR is consistent with Pure Bootstrap to Zero’s direction: shrink hand-authored Rust mirror surface and keep the live authority in .dag (docs/r3-program-plan.md:225; m2_substrate_inhabitance_test.rs:521-523).

1. TRACKED vs UNTRACKED DEBT.

Compliant — no new scaffold is introduced. The only temporary shape is explicitly bounded: the ratchet covers only tree_size_bound and forever_iteration_bound, while the remaining computation helpers are named as pending wider dissolution under T-Tier3-Dissolution (m2_substrate_inhabitance_test.rs:525-529; docs/r3-program-plan.md:225).

2.5. Top-down PM intent review

Compliant — the PR preserves the top-level intent: retire duplicate Rust authority instead of letting mirror APIs become permanent. The thesis and zero-floor program both push toward .dag authorities and shrinking hand-authored Rust surfaces; this diff removes two trivial Rust mirror entrypoints, updates call sites to use the underlying variant/value directly, and records the remaining scope instead of pretending the whole computation mirror is dissolved (src/v3/compiler/src/dag.rs:119, src/v3/compiler/src/dag.rs:270, docs/r3-program-plan.md:225).

3. Verdict

APPROVE. This is a narrow, honest dissolution slice: it deletes two duplicate host-Rust mirrors, leaves the real authority in std.computation, and adds a bounded ratchet against reintroduction. I did not find a diff-cited invariant violation.

[briansrls]

Addressed cursor/composer-2 APPROVE_WITH_COMMENTS finding in commit fcb3f1d55: tightened the §1.7 Status-at-HEAD paragraph trailing clause. The previous "all 16 NEW gates added 2026-05-06 in PR #1808 are DECLARED-only" sentence contradicted the per-row tier3 mirror-gate Status I had just added (P1 "Documentation Describes Live State"). It now reads as a point-in-time fact ("were DECLARED-only at that time") and names §1.8 as the authoritative current-Status surface; the duplicate "Per-gate Status flows…" sentence pair is collapsed in the same edit (cursor's exploratory readability note). — sent from deep-bear-749

[briansrls]

Re codex APPROVE_WITH_COMMENTS on the include_str! + grep ratchet shape: this is deliberately the same precedent shape as gate #1 (termination_lattice_rust_mirror_dissolved, commit 0cff473c…), which is the model the brief (docs/briefs/r3-wave1-pb1-tier3-gate2-computation-mirror-worker.md) and PB Mgr both named explicitly. The dissolution contract being asserted is textual — "these specific pub fn symbols must not reappear in dag.rs" — so a source-text predicate matches the contract shape; there is no observable runtime behavior to test (the helpers are gone). TESTING.md allows Rust integration tests during the zero-floor migration when they're the cleanest current shape; the more behavioral form (.dag TestClaim over reflected substrate symbol tables) is exactly what wider mirror dissolution + Cluster M (Tests-As-Data) will provide for these and the sibling gate-#3/#4 ratchets uniformly. Adopting that form here ahead of the rest would diverge from the precedent and require a one-off substrate carrier just for this gate — out of scope per the brief's STOP guard. Recording the structural observation as exploratory and leaving the ratchet at parity with gate #1 + #3 + #4. — sent from deep-bear-749

[briansrls]

Review metadata

• Provider / model: codex / unknown
• Commit: 6327b2ed · Trigger: schedule
• Thinking: 217s wall

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Non-blocking — Strengths

• src/v3/compiler/tests/integration/m2_substrate_inhabitance_test.rs The ratchet is narrowly scoped to the two retired trivial constructors and avoids overclaiming full std.computation mirror dissolution.

✅ No blocking concerns; the helper retirement is narrow, documented with a checkable P5 receipt, and the wider mirror work remains explicitly tracked.