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-0012-git-shard-adapter.md

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+---
+id: SHARD-WP-0012
+type: workplan
+title: "second adapter — git-IS-store shard (contract validation on a new substrate)"
+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-0008
+---
+
+# SHARD-WP-0012 — git-IS-store shard adapter
+
+## Goal
+
+Add a **second adapter on a different substrate** to validate the contract beyond the plain
+folder: a **git-IS-store** shard (`FederationArchitecture` T17 / TSD §A.3 — the home case where
+git is the store *and* the journal). It exercises git-native history (TSD §A.5 *adopt*),
+commit-as-write, `current_rev`=commit-sha drift detection, and the implication rules
+(attachment=git-IS-store ⟹ substrate=git ∧ history=git-native). Proves "writing an adapter +
+declaring a verified profile" is all it takes — no core changes.
+
+**Non-goal:** remote push/pull federation (VCS-replication+ping is a federation workplan);
+merge beyond fast-forward (apply-under-drift refuse is enough, as in SHARD-WP-0008).
+
+## Context
+
+- Contract: `TechnicalSpecificationDocument.md` §A; binding taxonomy §A.3; history §A.5.
+- Reuses the existing contract/conformance/overlay machinery unchanged.
+
+---
+
+## GitShardAdapter — read over a git working tree/repo
+
+```task
+id: SHARD-WP-0012-T1
+status: todo
+priority: high
+```
+
+A `GitShardAdapter` reading Markdown from a git repo: keys = tracked `*.md` paths; `read`
+returns a `Page` whose `source_rev` is the **commit sha** (HEAD or blob commit); profile =
+git-IS-store / substrate=git / history=git-native / addressing=path, validated against the
+implication rules. Tests: read tracked files; profile validates; conformance read path passes.
+
+## Write = commit; current_rev = sha (drift)
+
+```task
+id: SHARD-WP-0012-T2
+status: todo
+priority: high
+```
+
+`write(key, body)` stages + **commits** (author/message), returning the updated `Page` at the
+new sha; `current_rev(key)` returns the current commit sha for drift detection. Declare `WRITE`
++ `version`. Tests: write commits; conformance positive-write probe passes; `current_rev`
+changes after an external commit.
+
+## History adopt + integration with union/overlay
+
+```task
+id: SHARD-WP-0012-T3
+status: todo
+priority: medium
+```
+
+Adopt git-native history (TSD §A.5 *adopt*): expose a minimal page history (commit list for a
+path) behind a `version`-gated method. Integration: attach a `GitShardAdapter` to an
+`InformationSpace` alongside a `FolderAdapter` → resolve/chorus/edit/overlay/apply all work
+across substrates (apply-under-drift uses sha rev). Update SCOPE; `pytest` + pyflakes green.
+
+---
+
+## Acceptance criteria
+
+- `GitShardAdapter` passes the conformance suite (read + positive write) with a profile whose
+  implication rules hold (git-IS-store ⟹ git substrate + git-native history).
+- Write = commit; `current_rev` = sha drives apply-under-drift correctly.
+- The union/overlay/edit machinery works unchanged across folder + git shards (no core change —
+  capability-as-data proven on a second substrate).
+- `pytest` + pyflakes green; each task committed; state-hub synced.
+
+## Notes
+
+If `git` plumbing via subprocess proves heavy for tests, a thin in-repo git helper (or
+`tmp_path` repos created in tests) is acceptable; no new runtime dependency — use stdlib +
+`git` CLI already present.
+
+## Suggested task order
+
+T1 read adapter + profile → T2 write=commit + current_rev → T3 history adopt + integration.