fix(compaction): strip glued spine sentinel from long standing tokens

cutSpineGoal glues "..." onto a start-at-0 token longer than the
cap. outputFormatTokenRe eats that sentinel, so Goal and Output
harvests diverge and a without-file re-fold duplicates the token.
Strip the glued sentinel when restoring Output, and do not recut a
cap-length prefix that already ends with the sentinel.

Author: TheGreatAxios

src/session/compaction-handoff.test.ts

@@ -749,6 +749,74 @@ describe("iterative folding", () => {
     expect(withoutFile.artifact.goal).not.toContain(`${token} ${token}`);
   });
 
+  test("without-file re-fold of a start-at-0 FILES_DONE longer than 160 keeps one token", () => {
+    const token = `FILES_DONE=${"src/session/compaction-handoff.ts/".repeat(8)}end.ts`;
+    expect(token.length).toBeGreaterThan(160);
+    const goal = `${token} trailing prose after the standing token`;
+    const first = buildHandoffFold([userTurn(goal)], "narrative");
+    expect(first.artifact.goal).toBe(goal);
+    expect(first.spineText).toContain(`Goal: ${token}...`);
+    expect(first.spineText).toContain(`Output: ${token}`);
+
+    const withoutFile = buildHandoffFold(
+      [spineTurn(first.spineText), userTurn("Continue.")],
+      "narrative",
+    );
+    expect(withoutFile.artifact.goal).toBe(token);
+    expect(withoutFile.spineText).toContain(`Output: ${token}`);
+    expect(
+      withoutFile.spineText
+        .split("\n")
+        .find((line) => line.startsWith("Output: ")),
+    ).toBe(`Output: ${token}`);
+    expect(withoutFile.artifact.goal).not.toContain(`${token}... ${token}`);
+    expect(withoutFile.artifact.goal).not.toContain(`${token} ${token}`);
+  });
+
+  test("without-file re-fold of a start-at-0 comma-joined FILES_DONE keeps one token", () => {
+    const token = `FILES_DONE=${Array.from({ length: 20 }, (_, i) => `src/session/file${i}.ts`).join(",")}`;
+    expect(token.length).toBeGreaterThan(160);
+    const goal = `${token} trailing prose after the standing token`;
+    const first = buildHandoffFold([userTurn(goal)], "narrative");
+    expect(first.artifact.goal).toBe(goal);
+
+    const withoutFile = buildHandoffFold(
+      [spineTurn(first.spineText), userTurn("Continue.")],
+      "narrative",
+    );
+    expect(withoutFile.artifact.goal).toBe(token);
+    expect(
+      withoutFile.spineText
+        .split("\n")
+        .find((line) => line.startsWith("Output: ")),
+    ).toBe(`Output: ${token}`);
+    expect(withoutFile.artifact.goal).not.toContain(`${token}... ${token}`);
+    expect(withoutFile.artifact.goal).not.toContain(`${token} ${token}`);
+  });
+
+  test("two without-file re-folds of a 159-char spaceless prefix do not grow a fourth dot", () => {
+    const prefix = "A".repeat(159);
+    const goal = `${prefix} extra words beyond the spine cap`;
+    const first = buildHandoffFold([userTurn(goal)], "narrative");
+    expect(first.spineText).toContain(`Goal: ${prefix}...`);
+    expect(first.artifact.goal).toBe(goal);
+
+    const withoutFile = buildHandoffFold(
+      [spineTurn(first.spineText), userTurn("Continue.")],
+      "narrative",
+    );
+    const again = buildHandoffFold(
+      [spineTurn(withoutFile.spineText), userTurn("Continue.")],
+      "narrative",
+    );
+    expect(withoutFile.spineText).toContain(`Goal: ${prefix}...`);
+    expect(again.spineText).toContain(`Goal: ${prefix}...`);
+    expect(withoutFile.spineText).not.toContain(`${prefix}....`);
+    expect(again.spineText).not.toContain(`${prefix}....`);
+    expect(withoutFile.artifact.goal).not.toContain("....");
+    expect(again.artifact.goal).not.toContain("....");
+  });
+
   test("a truncated spine fragment collapses into the full prior-file constraint", () => {
     const full = `Must never ship without ${"x".repeat(80)}`;
     const first = buildHandoffFold([userTurn(full)], "narrative");

src/session/compaction-handoff.ts

@@ -153,6 +153,21 @@ function mergeStandingOutputToken(
 ): string {
   if (goal === undefined || goal.length === 0) return token;
   if (hasStandingOutputToken(goal, token)) return goal;
+  // cutSpineGoal glues "..." onto a start-at-0 token longer than the cap.
+  // outputFormatTokenRe (\S+) eats that sentinel, so Goal's harvested token
+  // is token+"..." and never equals the Output token. Strip the glued
+  // sentinel and keep the standing token once.
+  if (
+    goal.endsWith(SPINE_CUT_SENTINEL) &&
+    !token.endsWith(SPINE_CUT_SENTINEL)
+  ) {
+    const prefix = goal.slice(0, -SPINE_CUT_SENTINEL.length);
+    if (
+      hasStandingOutputToken(prefix, token) ||
+      outputFormatTokens(goal).includes(`${token}${SPINE_CUT_SENTINEL}`)
+    )
+      return prefix;
+  }
   const prefix =
     goal.endsWith(SPINE_CUT_SENTINEL) && !trailingEllipsisIsStandingToken(goal)
       ? goal.slice(0, -SPINE_CUT_SENTINEL.length)
@@ -163,6 +178,13 @@ function mergeStandingOutputToken(
 function cutSpineGoal(text: string): string {
   const line = text.replace(/\s+/g, " ").trim();
   if (line.length <= SPINE_GOAL_CHARS) return line;
+  // A prior spine cut already ended with the sentinel and sits at the cap.
+  // Recutting a 159-char spaceless prefix plus "..." eats the first dot and
+  // glues another sentinel, growing "..." into "....".
+  if (line.endsWith(SPINE_CUT_SENTINEL)) {
+    const without = line.slice(0, -SPINE_CUT_SENTINEL.length);
+    if (without.length <= SPINE_GOAL_CHARS) return line;
+  }
   let cap = SPINE_GOAL_CHARS;
   for (const match of line.matchAll(outputFormatTokenRe())) {
     const start = match.index ?? 0;