feat(proposalModel): setProposalApplied re-anchors + stores original (#64)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/proposalModel.ts

@@ -37,6 +37,25 @@ export function removeProposal(artifact: Artifact, proposalId: string): boolean
   return artifact.proposals.length < before;
 }
 
+/**
+ * F12/#64 (INV-48): record a proposal as optimistically applied — store the
+ * pre-apply `original` (for revert + the struck `<del>`) and re-point its anchor
+ * fingerprint to the now-in-buffer applied text so `resolve()` finds it. Idempotent
+ * shape: a second call simply overwrites with the same values.
+ */
+export function setProposalApplied(
+  artifact: Artifact,
+  proposalId: string,
+  appliedFp: Fingerprint,
+  original: string,
+): boolean {
+  const p = artifact.proposals.find((x) => x.id === proposalId);
+  if (!p) return false;
+  p.original = original;
+  artifact.anchors[p.anchorId] = { fingerprint: appliedFp };
+  return true;
+}
+
 /** Markdown comment body: instruction header + fenced whole-range diff. */
 export function proposalBody(targetText: string, p: Proposal): string {
   const header = p.instruction ? `**Claude proposes** — _${p.instruction}_` : "**Claude proposes**";

test/proposalModel.test.ts

@@ -9,7 +9,7 @@ import {
   type Proposal,
 } from "../src/model";
 import { CoauthorStore } from "../src/store";
-import { addProposal, proposalBody, removeProposal } from "../src/proposalModel";
+import { addProposal, proposalBody, removeProposal, setProposalApplied } from "../src/proposalModel";
 
 const agent = {
   kind: "agent" as const,
@@ -104,4 +104,19 @@ describe("proposalModel helpers (spec §6.4)", () => {
     expect(body).toContain("- old line two");
     expect(body).toContain("+ new only line");
   });
+
+  it("setProposalApplied stores original and re-anchors the fingerprint to the applied text", () => {
+    const a = emptyArtifact("docs/x.md");
+    const { proposalId, anchorId } = addProposal(
+      a,
+      { text: "old", before: "", after: "", lineHint: 0 },
+      "new",
+      { kind: "agent", id: "claude", agent: { sdk: "x", model: "m", sessionId: "s" } },
+      { granularity: "block" },
+    );
+    setProposalApplied(a, proposalId, { text: "new", before: "", after: "", lineHint: 0 }, "old");
+    const p = a.proposals.find((x) => x.id === proposalId)!;
+    expect(p.original).toBe("old");
+    expect(a.anchors[anchorId].fingerprint.text).toBe("new");
+  });
 });