#47 (SLICE-2, review): per-block document proposals + word-precise accept

Document-edit flow SLICE-2 (specs/coauthoring-document-edit-flow.md §7.2,
INV-39/40/41 — P1 "too much to review"). A whole-document rewrite now proposes
ONE F4 proposal per CHANGED BLOCK (the unit a human reviews), but accepting a
block reconciles attribution at WORD granularity (the unit F3 records). Block =
decision unit; word = attribution unit. Supersedes INV-37's per-word cut for
document edits; selection edits unchanged.

- trackChangesModel.ts: new pure diffToBlockHunks(current, rewritten) — block-key
  alignment (reusing diffArrays/diffBlocks keying): an isolated changed block →
  one block-aligned hunk → the rewritten block raw (a code/mermaid fence is one
  atomic whole-fence hunk, INV-23); insert/delete runs → one gap-span hunk over
  the inter-anchor region (separators included) so reconstruction stays exact; a
  zero-width gap-span is anchored (INV-41). Also split diffToHunks into the raw,
  un-anchored wordEditHunks + the anchoring wrapper (the anchoring could grow an
  insertion to overlap an adjacent hunk, corrupting a batch apply — a latent bug
  that only surfaced once hunks are applied as a batch).
- trackChangesPreview.ts: runEditAndPropose document branch uses diffToBlockHunks
  and tags each proposal granularity:"block".
- model.ts / proposalModel.ts: additive optional Proposal.granularity
  ("block"|"single"; absent ⇒ single, back-compat — no migration).
- proposalController.ts: accept of a block proposal runs an intra-block word
  sub-diff (wordEditHunks, disjoint) and applies one applyAgentEdit per changed
  run, descending offset — only the words Claude changed land Claude-attributed;
  unchanged spans keep prior authorship (INV-40).
- Tests: diffToBlockHunks unit (reconstruction + fence atomic + add/remove);
  f12Review host E2E (M blocks→M proposals, unchanged→none, fence atomic, INV-40
  attribution, INV-41 insertion accept); updated the f11 document-path E2E to
  per-block (INV-39 supersedes INV-37); MANUAL-SMOKE-F12 §2.

Seam note: pendingEdits.matchEvent resolves one registration per change event, so
INV-40's per-run attribution is sequential applyAgentEdit calls (N undo steps),
not one multi-replace WorkspaceEdit — see transcript Deferred decisions.

214 unit + 69/5 host E2E green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/trackChangesPreview.ts

@@ -13,7 +13,7 @@ import * as vscode from "vscode";
 import type { DiffViewController } from "./diffViewController";
 import type { AttributionController } from "./attributionController";
 import type { ProposalController } from "./proposalController";
-import { renderReview, renderPlain, diffBlocks, diffToHunks, type BlockOp } from "./trackChangesModel";
+import { renderReview, renderPlain, diffBlocks, diffToBlockHunks, type BlockOp } from "./trackChangesModel";
 import { buildFingerprint } from "./anchorer";
 import { isAuthorable } from "./workspacePath";
 import type { EditTurnResult } from "./liveTurn";
@@ -226,11 +226,12 @@ export class TrackChangesPreviewController implements vscode.Disposable {
   }
 
   /**
-   * F11 (INV-35/37): run one host edit turn and record the result as F4
+   * F11/F12 (INV-35/39): run one host edit turn and record the result as F4
    * proposal(s) — a SELECTION yields one single-range proposal over the resolved
-   * block-union; a DOCUMENT rewrite is `diffToHunks`'d into one single-range
-   * proposal per changed hunk (reusing the F4 single-range model N times, no new
-   * model). Never mutates the document (INV-10). Returns the created proposal ids.
+   * block-union; a DOCUMENT rewrite is `diffToBlockHunks`'d into one proposal per
+   * changed BLOCK (#47, INV-39 supersedes INV-37's per-word cut), each tagged
+   * `granularity:"block"` so accept reconciles attribution per word (INV-40).
+   * Never mutates the document (INV-10). Returns the created proposal ids.
    */
   async runEditAndPropose(
     document: vscode.TextDocument,
@@ -253,9 +254,17 @@ export class TrackChangesPreviewController implements vscode.Disposable {
     }
     const turn = await this.editTurn(instruction, full);
     const ids: string[] = [];
-    for (const h of diffToHunks(full, turn.replacement)) {
+    // #47 (INV-39, supersedes INV-37): a document rewrite is cut at BLOCK
+    // granularity — one proposal per changed block (the unit a human reviews) —
+    // not per word. Each is tagged `granularity:"block"` so accept reconciles
+    // attribution per word inside the block (INV-40).
+    for (const h of diffToBlockHunks(full, turn.replacement)) {
       const fp = buildFingerprint(full, { start: h.start, end: h.end });
-      const id = await this.proposals.propose(document, fp, h.replacement, provenance(turn), { turnId, instruction });
+      const id = await this.proposals.propose(document, fp, h.replacement, provenance(turn), {
+        turnId,
+        instruction,
+        granularity: "block",
+      });
       if (id) ids.push(id);
     }
     return ids;