Cut D PR 2a: pair-serving authority on its own event-log partition, read by every effectful consumer

[gunbai-bot]

Summary

Second Cut D PR (docs/plans/dsv41-cut-d-redesign.md). D0 must move Group A through Active → SuspensionPendingReconciliation → SuspendedForAuthorizedSuccessor under a lease, and a pure fold returning the next state changes nothing a consumer reads. This lands the store and routes the effectful consumers through it; D0 itself (incumbent-first question, occupancy reconciliation, LeaseGrant↔HeldLease join, entry receipt, baseline contract) is PR 2b.

Design call (agreed with operator): the source row spark_pair_serving_authorities stays the claim and resting authority — membership is pure and suspension keeps the claim. The log carries open-transaction state, folded from the resting row. Empty partition ⇒ the authored resting state governs; unreadable partition ⇒ every effectful consumer refuses, never falls back to the row.

Store: DESIGN §3b puts serving-side occupancy on the event chain, so the authority goes on gunbc.fabric_event_log partition pair-serving-authority/<group> — same leased-push CAS as seats.

• gunbc.fabric_event_log — read/append generic in the payload (*_with take encode/decode); PoolEvent entries are specializations. No caller churn.
• product.capacity.event_json — chain envelope codec once, for any payload; pool_events consumes it. EventDecode<P> replaces PoolEventDecode.
• gunbc.spark.pair_serving_authority_log — codec for all five arms (flat prev_/next_ members); authority_fold refuses an event leaving a non-current state or naming another group; current_pair_serving_authority; pair_serving_authority_transition — one CAS, no retry (a stale transition returns the now-current state; unlike a seat the decision must be re-made).
• Consumers: spark_pair_serving_apply_wet plans under the executor's live authorities; fabric_capacity_standing reads them. Both keep a supplied-roster seam (*_current) their witnesses drive at generation 0.
• std.content_hash.parse_content_hash — wire inverse moved to the grammar's home (was materialization_object.parse_recorded_store_key); wire inverses for HeldLeaseObservedState, FabricGroup beside their wire forms.

Test plan

• pair_serving_authority_log_witness (hermetic): every arm round-trips; wire distinguishes arms/fields; foreign/incoherent doc refuses; fold walks from resting through transitions (gen 0 → 2); fold refuses non-current previous at that event; refuses cross-group next. 6/6 PASS.
• pair_serving_authority_log_real_execution_witness (wet lane, enrolled in ci_layer_roots / local_repo_wet_terminal / floor_route_gap): against a bare remote — empty log reads resting at gen 0; transition appends and reads back at gen 1; a second transition expecting the resting state is Stale carrying the current, appends nothing; unclaimed group refuses at claim. 2/2 PASS.
• Touched witnesses re-run and passing: capacity standing (live entry via supplied roster), apply plan, authority seam, pool-event codec round-trip, store-key round-trip + trailing-prefix refusal, event-log append real execution.
• Pre-existing, untouched: spark_pair_serving_apply_witness.every_promoted_group_plans_and_the_second_is_group_b_headed_by_srv9 fails identically on clean origin/main (expects two groups; roster has one since DS4.1 #11501).

🤖 Generated with Claude Code

[gunbai-bot]

Transition-admission migration for gunbc#11704. No action until the operator sequences #11704's landing.

gunbc#11704 moves namespace transition admissions out of the tree. Once it lands, any file under dag/gunbc/namespace/transition_admission/ refuses at this PR's own gate, and the admission has to be carried in a commit message on this branch instead. The block below was derived mechanically from this PR's 2 row file(s) at its current head. The only edits: deletion_follow_up, owner_pull_request and their now-unused imports are dropped, because those fields no longer exist. All 2 blocks load through the production fold (carried_admissions_from_messages) with no refusal.

To migrate (paste + delete), after #11704 is on main and merged into this branch:

git rm \
  dag/gunbc/namespace/transition_admission/product_capacity_pool_events_pool_event_kind_decode_member_nat_event_json.dag \
  dag/gunbc/namespace/transition_admission/product_capacity_pool_events_pool_event_kind_decode_member_nonempty_event_json.dag
git commit -F msg.txt   # msg.txt = the text below, verbatim

-F keeps the lines exactly as they are. The squash merge carries the message into the queue run, and nothing lands in the tree. If a row is wrong later, a later block with the same stem supersedes it.

msg.txt

Move transition admissions into the commit message (gunbc#11704)

```transition-admission
module gunbc.namespace.transition_admission.product_capacity_pool_events_pool_event_kind_decode_member_nat_event_json

import std.types { NonEmptyStr, List }
import std.decl_ref { decl_ref }
import gunbc.compiler_frontend_program_interlock { TargetChanged }
import gunbc.namespace.transition_admission { TransitionAdmission, Binding }

data product_capacity_pool_events_pool_event_kind_decode_member_nat_event_json: TransitionAdmission = TransitionAdmission {
  label: "Cut D 2a: the chain-envelope JSON codec moves to product.capacity.event_json; pool_events consumes member_nat from there" as NonEmptyStr,
  subject: Binding {
    enclosing: decl_ref("product.capacity.pool_events", "pool_event_kind_decode"),
    spelling: "member_nat" as NonEmptyStr,
    expected_candidates: [decl_ref("product.capacity.event_json", "member_nat")],
  },
  disposition: TargetChanged,
}
```

```transition-admission
module gunbc.namespace.transition_admission.product_capacity_pool_events_pool_event_kind_decode_member_nonempty_event_json

import std.types { NonEmptyStr, List }
import std.decl_ref { decl_ref }
import gunbc.compiler_frontend_program_interlock { TargetChanged }
import gunbc.namespace.transition_admission { TransitionAdmission, Binding }

data product_capacity_pool_events_pool_event_kind_decode_member_nonempty_event_json: TransitionAdmission = TransitionAdmission {
  label: "Cut D 2a: the chain-envelope JSON codec moves to product.capacity.event_json; pool_events consumes member_nonempty from there" as NonEmptyStr,
  subject: Binding {
    enclosing: decl_ref("product.capacity.pool_events", "pool_event_kind_decode"),
    spelling: "member_nonempty" as NonEmptyStr,
    expected_candidates: [decl_ref("product.capacity.event_json", "member_nonempty")],
  },
  disposition: TargetChanged,
}
```

[gunbai-bot]

Closed per operator decision (2026-09-20): main's #11723 replaced git under the fabric event log; this PR's diff is carried by #11555, which is being re-realized on the fabric DB. — sent from proud-deer-538