workplans: register follow-up implementation roadmap (WP-0009..0012)

WP-0009 git-backed DecisionLog + per-space append authority (keystone backing);
WP-0010 derived views (wikilinks, BackLinks, RecentChanges, AllPages/SiteMap);
WP-0011 incremental union + equivalence index + I-2 verification;
WP-0012 second adapter (git-IS-store) validating the contract on a new substrate.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

workplans/SHARD-WP-0011-incremental-union.md

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+---
+id: SHARD-WP-0011
+type: workplan
+title: "incremental union maintenance + equivalence index + I-2 verification"
+domain: whynot
+repo: shard-wiki
+status: active
+owner: tegwick
+topic_slug: whynot
+created: "2026-06-15"
+updated: "2026-06-15"
+depends_on:
+  - SHARD-WP-0007
+  - SHARD-WP-0010
+---
+
+# SHARD-WP-0011 — Incremental union + equivalence index
+
+## Goal
+
+Replace direct, recompute-on-read resolution with the **incremental-first** derived tier from
+`CoreArchitectureBlueprint` §8.7: change-driven delta maintenance of the union/indexes, an
+**indexed equivalence** path (blocking/LSH, not O(N²)) with correct retraction/propagation
+(review B-4), and the **I-2 verification** mechanism (digest + background consistency-checker).
+Rebuild becomes a bounded fallback, not the operational path.
+
+**Non-goal:** distributed maintenance; persisted on-disk index store (in-memory derived tier is
+fine for this slice). Per-tenant partitioning (I-13) is honoured structurally but multi-tenant
+deployment is later.
+
+## Context
+
+- Spec: blueprint §8.7 (incremental, blocking/LSH, rebuild-as-fallback), §8.4; review B-4 +
+  open items O-1/O-4.
+- Builds on union resolution (SHARD-WP-0007) and the views (SHARD-WP-0010) it accelerates.
+
+---
+
+## Equivalence index: blocking + verify
+
+```task
+id: SHARD-WP-0011-T1
+status: todo
+priority: high
+```
+
+A candidate-generation (**blocking**) layer — normalized title/path buckets + MinHash/LSH bands
+over content shingles — then **verify** (fingerprint / span-set overlap + curator bindings) to
+produce equivalence edges. Replaces pairwise O(N²). Tests: near-duplicates bucket together;
+unrelated pages don't; verified edges match a brute-force oracle on a small corpus.
+
+## Incremental maintenance (delta, not additive)
+
+```task
+id: SHARD-WP-0011-T2
+status: todo
+priority: high
+```
+
+Change-driven delta updates: a changed/added/removed page **re-buckets**, then (per B-4)
+**retracts** edges it leaves, **adds** edges it enters, and **propagates** to equivalence
+neighbours (a retraction can split a chorus set). Drives union/BackLinks/RecentChanges deltas.
+Tests: add/edit/remove keep the index equal to a from-scratch rebuild; a bucket-exit retracts a
+stale edge.
+
+## I-2 verification: digest + consistency-checker
+
+```task
+id: SHARD-WP-0011-T3
+status: todo
+priority: high
+```
+
+A per-partition **Merkle-style digest** of the derived tier, maintained alongside deltas, and a
+**background consistency-checker** that recomputes a sampled fold and compares; mismatch →
+**scoped recompute** of the affected region (self-healing). Makes `derived = f(canonical)`
+*verified*, not asserted. Tests: induced drift is detected and repaired; digest stable under
+equivalent event orders.
+
+## Wire incremental tier behind resolution + views
+
+```task
+id: SHARD-WP-0011-T4
+status: todo
+priority: medium
+```
+
+Route `UnionGraph.resolve` and the SHARD-WP-0010 views through the maintained index (rebuild =
+explicit fallback). Behaviour is unchanged from the consumer's view; only freshness/cost change.
+Update SCOPE; `pytest` + pyflakes green.
+
+---
+
+## Acceptance criteria
+
+- Equivalence is indexed (blocking/LSH + verify), not pairwise; matches a brute-force oracle.
+- Incremental maintenance (with retraction + propagation) keeps the derived tier equal to a
+  from-scratch rebuild; rebuild is a bounded fallback.
+- I-2 is verified by a digest + consistency-checker that detects and self-heals drift.
+- Consumer-visible resolution/views behaviour unchanged; `pytest` + pyflakes green; synced.
+
+## Suggested task order
+
+T1 equivalence index → T2 incremental maintenance → T3 I-2 verification → T4 wiring.