Every topology commit re-derives ~330 lines of header presentation because header state has nowhere to live but the commit path

Sub of #18304 (Workspace decomposition). Blocked by #18303 — needs that lane's Group provider to exist. (2026-09-05: the Group provider is PR #18360 / #18310 — Neo.manager.Transaction#getProvider(groupId); this leaf is gated on its merge.) (2026-09-05: dissolved — header state binds to the workspace's own provider, see the ledger; #18310 / PR #18360 landed first regardless.)

The Problem

Census amended 2026-09-05 by @neo-fable (assignee), read at dev 27e23b1084 / c5f02345e8: #18306 (PR #18347) extracted the syncDock* methods this section counted into src/dashboard/dock/projection/HeaderActionPolicy.mjs. Workspace.mjs now has 0 syncDock* definitions; it drives the policy from 11 call sites, and every topology commit runs the policy's syncAll twice on the settled tree (:3028, :3035) plus once after the refresh promise settles (:1949) — each pass = 5 syncs × every projected tab + syncLockRails, every write change-guarded. The re-derivation the paragraph below describes is intact; only its home moved. Original text kept for provenance:

syncDock* has 33 call sites in Workspace.mjs. @neo-fable's cluster census puts the re-derivation at ~330 lines swept per topology commit, setActiveItem included. The reason is structural rather than careless: header state has no home except the commit path, so every commit recomputes presentation that mostly did not change.

@neo-opus-vega's receipt (discussioncomment-18289767) narrowed what is actually destroyed today — no action button, tab button, toolbar or tab container is destroyed by any commit class, and retained containers never receive a headerActions assignment. So this is not a destruction defect; it is a re-derivation defect, and it disappears only when header state has an owner that outlives the commit.

The popup-birth arm showed the target already resolves correctly: header state read from the Group provider resolves identically from any window.

The Fix

Bind header state to the Group's StateProvider (owned by #18303) and delete the per-commit syncDock* sweeps that exist only to recompute it. Presentation reads state; it stops being recomputed by the mutation path.

This is the third of the three deletion budgets D#18150's step 1 named — (a) stand-ins for items with live panes, landed via #18274/PR #18279; (b) the staged shell on stable topology, retainTopology as default admission, gated on the rail reconcile #18320 owns; (c) these sweeps.

Contract Ledger Matrix

Acceptance Criteria

• Header state is read from the workspace's own state provider (dock.* on Workspace#stateProvider, chained upward by the ordinary hierarchy); the HeaderActionPolicy per-commit sweeps that exist solely to re-derive it are deleted in the same PR. (Amended 2026-09-05 — originally "read from the Group provider"; see the ledger row and the Avoided Traps note.)
• Measure executed header-policy evaluations before and after. A geometry-only change, and a transaction affecting another Workspace with unchanged local header inputs, must not trigger a full local header-policy sweep. The PR body carries the callback-count controls; source-line reduction alone is not performance evidence.
• Header state resolves identically from the opener and from a popped-out window — the popup arm's result, re-run as a permanent arm.
• toolbar.Base#syncActions is untouched.
• Behaviour is unchanged: focus-gated reveal, frozen action order, and per-pane enablement all identical before and after on the dock example and the Workstation. Changed active item, item policy, or runtime reload start/settlement updates the affected retained controls; preserve the existing asynchronous DockReload witness, including state changes without a document commit.

Out of Scope

• Moving the policy itself — that is #18306, and it lands first.
• retainTopology as default admission — gated on the rail reconcile #18320 owns; separate leaf, separate lane.
• Any change to the Group provider's own shape (#18303).

Avoided Traps

• Starting before #18303's Group exists. There is no provider to bind to; a stand-in provider here would be a second authority, which is the failure #18303's own ledger was written to prevent. (2026-09-05: the workspace's own provider is not a stand-in for the Group's — it is the tree node header truth belongs to; Group-wide truth keeps its one authority.)
• Deleting the sweeps without the binding. That removes the recomputation and the correctness together.

Related

#18304 (epic) · #18303 (blocker — owns the Group provider) · #18306 (policy vehicle, lands first) · #18320 (rail reconciliation) · #18274 → PR #18279 (step 1a, landed) · D#18150 DC_kwDODSospM4BFxvy

Runtime correctness control: NEO_INLINE_CODE_46. Reload flight state changes header enablement without changing the dock document, so document-only invalidation cannot replace this behavior.

Live latest-open sweep: latest 20 open issues at 2026-09-04T18:12Z; no equivalent. A2A claim sweep: no claim. Own-assignment sweep: none on this surface. Memory Core: stale-2025 recall degradation today — null, not clean.

Decision Record impact: depends-on — consumes #18303's Group contract; amends nothing.

Origin Session ID: b983b2a8-18bc-4dd0-a63f-23380dc3a49d