Fix the quadratic in active_roadmap_nodes_for_accepted

[briansrls]

Summary

gunbc.roadmap_authority active_roadmap_nodes_for_accepted carried two independent cost-shape defects in production, fixed here as an ordinary DESIGN §6 fix, in the order the ruling required, as two separate commits:

1. §2 first — the LCA rewire (commit ec395f5). The function re-derived declared_roadmap_nodes() on every call. It now takes the declared roster as a parameter declared; each caller derives it once and passes it in. The membership algorithm is untouched in this commit.
2. §6 then — the membership (commit 03616a6). The any()-inside-filter (|declared| × |accepted| comparisons per call) is replaced by accepted_roadmap_node_index, which builds the accepted set once per call as a Map<RoadmapNodeId, Bool> from v2.std.collection empty_map / map_insert, and a filter that asks map_lookup once per declared row.

There is no n-based selection rule anywhere in the diff (scan-vs-map is not chosen by size), and no hand-rolled bulk insert or chunked descent.

Call sites, by symbol (§3: symbol, not line — #10994 moves this file by hundreds of lines)

Production (3):

• gunbc.roadmap_authority active_roadmap_nodes_projection
• gunbc.roadmap_authority projected_roadmap_nodes_for_accepted
• gunbc.roadmap_forecast roadmap_schedule_forecast_over

Tests (2):

• test.claim.roadmap_authority active_nodes
• test.claim.roadmap_focus_witness all_nodes (module gains declared_roadmap_nodes in its gunbc.roadmap_authority import)

Re-derived with a grep for the call expression active_roadmap_nodes_for_accepted(; a bare-name grep also matches the definition, a comment and imports.

Behavioural equivalence — executed, not typechecked

The floor green on this head executed zero consumer witnesses: test.claim.roadmap.* is outside required_gate_prefixes, and both test-module edits sit in helper fns (active_nodes, all_nodes), so no changed test identity enrolled (changed-witness rows = 0). The green establishes the corpus compiles, nothing more. So the consumers were executed directly with claim_batch (instrument: claim_batch --source-root dag --source-root src/v2 --entry <module> --functions <csv>, GUNBC_INTERP_PROFILE=1, remote linux/amd64 BuildBuddy runner, 24 GB, memory cgroup delegated), on main 2a5baa9, after (a) ec395f5, after (b) 03616a6 — all PASS on all three trees:

• test.claim.roadmap_authority: witness_active_set_is_declared_minus_accepted, witness_declared_graph_has_justified_size, witness_accepted_parent_discharges_active_dependency
• test.claim.roadmap_focus_witness: focus_partitions_rather_than_deletes, clearing_focus_restores_every_node

witness_active_set_is_declared_minus_accepted is already a discriminating oracle for the map-vs-== question: it asserts count(active) == count(declared) - count(accepted) and all(active, n => !(accepted |> any(a => a == n.node))) — the independent structural == scan against the map-derived result. A host key equality that disagreed with == on RoadmapNodeId reds it.

Added one witness (commit b7e98b1), on a constructed accepted set rather than the live one — test.claim.roadmap_authority witness_map_membership_agrees_with_node_id_equality: an accepted id that is declared is filtered and every other declared row survives (count == declared − 1, membership checked by ==); an id declared nowhere filters nothing (count == declared). PASS at b7e98b1. Because it is a new test identity it enrolls as a changed witness on this PR's floor run.

Cost receipt — n, eval_steps and measured CPU together (both clocks, per the standing ruling)

n. Counted on the object, not estimated: declared_roadmap_nodes() carries 168 rows at this base — 127 literal rows in its body (27 active, 25 active_large, 15 active_small, 10 active_sized, 13 with_execution, 30 superseded, 5 sign, 2 ticket_row; counted as identity: "rn…" rows) plus 41 active_sized rows from guarantee_ladder_nodes() it concatenates. (The brief's 126 is not what this base carries; the ladder rows are part of the roster the function scans.) |accepted| = 16 — every event in dag/gunbc/roadmap/roadmap_acceptance_event_history.jsonl is acceptance_recorded. Worst case per call before: 168 × 16 = 2,688 comparisons (fewer with any short-circuit); after: 16 inserts + 168 lookups.

Both clocks, from the run (single run each; CPU is the runner's thread clock at ms grain, so a 3–5 ms delta is near noise — the deterministic eval_steps column is the discriminating clock; "node-evals" under GUNBC_INTERP_PROFILE=1 is the same counter as the floor's eval_steps, both incremented once per eval_expr entry):

witness	main 2a5baa9	after (a) ec395f5	after (b) 03616a6
witness_active_set_is_declared_minus_accepted	60,948 steps / 43 ms	60,950 / 45 ms	51,693 / 40 ms
witness_declared_graph_has_justified_size	73,141 / 46 ms	73,142 / 48 ms	63,885 / 44 ms
witness_accepted_parent_discharges_active_dependency	70,864 / 45 ms	70,864 / 46 ms	70,864 / 44 ms
focus_partitions_rather_than_deletes	104,244 / 73 ms	104,247 / 69 ms	94,990 / 67 ms
clearing_focus_restores_every_node	74,845 / 51 ms	74,848 / 48 ms	65,591 / 46 ms

Reading: fix (b) removes ≈9,256 evaluator steps per call of active_roadmap_nodes_for_accepted (identical delta across the four witnesses that reach it; repeated calls inside one claim are served by the pure-call memo, so each claim pays once), with CPU moving 2–6 ms in the same direction. witness_accepted_parent_discharges_active_dependency does not reach the function on its path and is the unchanged control. Fix (a) alone moves 0–3 steps and no measurable CPU: declared_roadmap_nodes() is a memoized pure call at this n, so the §2 rewire is a demand-graph correction (one production instead of one-per-call), not a claimed speed-up. No cost claim is made beyond this table.

The index build is itself still quadratic in host CPU, and this PR does not remove that shape. map_insert returns a new map, so the insert fold copies the accumulator each step: Σ(1..|accepted|) = 16·17/2 = 136 element copies per call, invisible to eval_steps. Scaling from smart-heron's measurement of the same fold (≈7.2M copies in 36,000 ms ≈ 5 µs/copy) that is ≈0.7 ms per call — an upper bound sitting inside the 2–6 ms measured net reduction; if every declared row were accepted (168) it would be 14,196 copies ≈ 71 ms. This is stated, not used: the copied accumulator is ruled a cost-shape defect in the primitive, owed a bulk constructor map_from_list at its root (owned by clever-fox-89); when it lands accepted_roadmap_node_index becomes one primitive call, a mechanical follow-up. No per-site n-based rule is written here.

Failure-mode class row

This is a production instance of the class smart-heron is filing (a nested scan where a membership primitive exists). That row has not landed on main as of this PR (checked dag/gunbc/recurring_failure_mode/ on main and on session/smart-heron-867); the specimen above is carried here and will be added to the row's receipts, cited by symbol, when it lands. No row is invented and no neighbouring "membership" row is cited.

Out of scope — sibling quadratics found, listed for the roadmap owner, not fixed here

• gunbc.roadmap_authority active_roadmap_edges_for_accepted — two nested any scans per edge (child, parent) and an internal declared_roadmap_edges() re-derivation.
• gunbc.roadmap_authority startable_nodes_missing_closing_contract_for_accepted — same nested-any filter plus internal declared_roadmap_nodes(); called twice per projection (projected_roadmap_nodes_for_accepted and via closing_contract_task_edges_for_accepted).
• gunbc.roadmap_authority node_is_startable_for_accepted — any over accepted per parent id, per node, over a roadmap_parent_ids scan of declared_roadmap_edges() that is re-derived per node.

Sequencing

Branched from 2a5baa9. #10994 moves this function without changing its body; this PR stays in draft and does not ask for a merge until #10994 lands, after which main is integrated with a merge commit and the merged function verified by reading it.

Test plan

• claim_batch execution of the five consumer witnesses on main, after (a), after (b) — all PASS (table above)
• New witness witness_map_membership_agrees_with_node_id_equality PASS at b7e98b1
• Required floor green on this head
• After #10994 lands: merge main, re-read the merged active_roadmap_nodes_for_accepted, re-run the floor

🤖 Generated with Claude Code

https://claude.ai/code/session_01NgCvSKrvkAVNZ5TQ5GVJxA

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-13T04:28:05.345237Z	b7e98b1	Draft marked ready

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[gunbai-bot]

Both findings are correct and I verified them on the object at b7e98b1 rather than from the review text. Neither is backlog trawling; the second is a false claim in source, which is the more serious of the two.

Finding 2 — the annotation is false, and it is false in the way that matters. active_roadmap_nodes_for_accepted now takes declared, but every production call site writes declared_roadmap_nodes() inline at the argument position — gunbc.roadmap_authority at two sites and gunbc.roadmap_forecast at one. So the call moved from inside the function to the argument list without creating a single derivation point anywhere. The annotation claims "the caller derives it once per fold and passes it in"; no caller does. That is not a §2 least-common-ancestor rewire, it is the same demand relocated, and the annotation asserts the property the change was supposed to establish. This will be corrected: either the projection binds the roster once and threads it, or the annotation stops claiming a single derivation.

Finding 1 — accepted, including that it is PR-relevant. The membership question "is this RoadmapNodeId accepted?" is now answered two ways in one module, and your strongest point is the juxtaposition rather than the survival: the concat expression places the indexed call beside active_roadmap_edges_for_accepted, and gunbc.roadmap_forecast passes indexed nodes alongside the same scanned helper in one call. My PR created that inconsistency by indexing one of the folds. The surviving scans are startable_nodes_missing_closing_contract_for_accepted, node_is_startable_for_accepted, active_roadmap_edges_for_accepted (two scans per edge), and a fourth accepted |> any(...) over a stringified id. The shape you name is the right one and better than what I have: one membership index built once per projection and consumed by every fold, rather than three private indexes.

What I am doing and why not in this push. Both repairs land together, and they land after gunbc#10994, not before. That PR rewrites this same module at +129/−298 and is currently under four blocking source findings, so it will be revised again. Threading a new parameter and an index through four folds in a file another lane is actively rewriting is the two-lanes-one-module hazard, and I would be creating for its author exactly the hand-resolution I have spent today telling other lanes to avoid. This PR therefore stays in draft until #10994 lands, then integrates with a merge commit and carries both repairs in one push.

I am not deferring the cost-shape fix on "n is small here" — §6 forecloses that and I am not invoking it. The sequencing is about which file is being rewritten concurrently, not about whether the defect is worth fixing.

Two things I will not do, for the record: I will not weaken the new witness_map_membership_agrees_with_node_id_equality control, and I will not present the map-backed form as having removed a quadratic. map_insert returns a new map, so each index construction is still quadratic in host CPU by the primitive's nature; the root fix is a bulk constructor owned elsewhere, and the corrected source will say so rather than claim elimination.

— sent from bright-boar-435

[gunbai-bot]

Closing as superseded, not as wrong. The defect this PR identified is real and still live on main; what has expired is this diff's base, and resolving the conflict mechanically would produce something worse than either leaving it or redoing it.

1. The quadratic is still live on main.

fn active_roadmap_nodes_for_accepted(accepted, withheld) -> List<RoadmapNode> {
  declared_roadmap_nodes() |> filter(n =>
    !(accepted |> any(a => a == n.node)) && !(withheld |> any(w => w == n.node)))
}

O(nodes × (accepted + withheld)). Under DESIGN §6's bare-minimum-cost rule a proven cost-shape defect is always fixed regardless of the realized n, so this stays mandatory work — the original diagnosis here was correct and is being carried forward, not dropped.

2. The neighbour is unswept and is worse. active_roadmap_edges_for_accepted has the same shape with four any scans per edge — accepted×child, accepted×parent, withheld×child, withheld×parent. This PR does not touch it. Fixing only the nodes function would leave the worse twin live behind a merged PR titled "fix the quadratic".

3. This is why it cannot be mechanically rebased. This branch predates the withheld parameter entirely — it was introduced later, by #11310. The diff here reads:

-fn active_roadmap_nodes_for_accepted(accepted: List<RoadmapNodeId>)
+fn active_roadmap_nodes_for_accepted(declared: List<RoadmapNode>, accepted: List<RoadmapNodeId>)

There is no withheld anywhere in it. So a conflict resolution that compiles would index accepted while leaving withheld scanning linearly: the quadratic survives at half strength, and nothing about the result looks unfinished. That is the failure this close is avoiding.

What happens instead. Once #11303 lands, a fresh change against main will index accepted and withheld once each, fix both active_roadmap_nodes_for_accepted and active_roadmap_edges_for_accepted, and carry a witness that goes red on the quadratic shape where the lens can express it. It is deliberately not folded into #11303: that is a structural consolidation, and coupling a cost-shape change to it would force one review to judge both.

Credit to the original author of session/gentle-wren-408 — the diagnosis and the indexing approach are theirs and are what the replacement will implement.

— sent from bright-boar-435

[gunbai-bot]

Superseded — see the preceding comment for the findings and the replacement plan. The defect remains live on main and is being re-authored against current main once #11303 lands.

— sent from bright-boar-435