fix(shared): PRs built on the same PR stay in one stack under their parent

apps/mobile/src/features/threads/git/GitOverviewSheet.tsx

@@ -379,7 +379,11 @@ function GitOverviewSheetContent(props: GitOverviewSheetProps) {
                 </View>
               ) : null}
               {chain.layers.map((link, index) => (
-                <View key={threadPullRequestKeyOf(link)}>
+                <View
+                  key={threadPullRequestKeyOf(link)}
+                  // Steps in per layer like the web list, capped so deep stacks keep their width.
+                  style={{ paddingLeft: Math.min(chain.depths[index]!, 3) * 16 }}
+                >
                   {index > 0 && Platform.OS !== "android" ? (
                     <View className="ml-12 h-px bg-border" />
                   ) : null}

apps/server/src/mcp/toolkits/pullRequests/handlers.test.ts

@@ -579,6 +579,22 @@ describe("listThreadPullRequests", () => {
     ]);
     expect(result.chains).toEqual([{ kind: "native", numbers: [1, 2] }]);
   });
+
+  it("gives pull requests built on the same one the same position", () => {
+    const result = listThreadPullRequests({
+      pullRequests: [
+        makeLink(1, { headBranch: "feat-a", baseBranch: "main" }),
+        makeLink(2, { headBranch: "feat-b", baseBranch: "feat-a" }),
+        makeLink(3, { headBranch: "feat-c", baseBranch: "feat-a" }),
+      ],
+    });
+    expect(result.pullRequests.map((entry) => [entry.number, entry.stack])).toEqual([
+      [1, { kind: "derived", position: 1, size: 3 }],
+      [2, { kind: "derived", position: 2, size: 3 }],
+      [3, { kind: "derived", position: 2, size: 3 }],
+    ]);
+    expect(result.chains).toEqual([{ kind: "derived", numbers: [1, 2, 3] }]);
+  });
 });
 
 describe("pull request guide tools", () => {

apps/server/src/mcp/toolkits/pullRequests/handlers.ts

@@ -122,7 +122,7 @@ function entryOf(
     if (chain.layers.length < 2) continue;
     const index = chain.layers.findIndex((layer) => threadPullRequestKeyOf(layer) === key);
     if (index !== -1) {
-      stack = { kind: chain.kind, position: index + 1, size: chain.layers.length };
+      stack = { kind: chain.kind, position: chain.depths[index]! + 1, size: chain.layers.length };
       break;
     }
   }

apps/server/src/mcp/toolkits/pullRequests/tools.ts

@@ -255,7 +255,7 @@ export const ThreadPullRequestEntry = Schema.Struct({
   stack: Schema.NullOr(
     Schema.Struct({
       kind: Schema.Literals(["native", "derived"]),
-      /** 1-based, bottom of the stack first. */
+      /** 1-based layer, bottom of the stack first. Pull requests built on the same one share it. */
       position: Schema.Int,
       size: Schema.Int,
     }),
@@ -268,7 +268,7 @@ export const ListThreadPullRequestsResult = Schema.Struct({
   chains: Schema.Array(
     Schema.Struct({
       kind: Schema.Literals(["native", "derived"]),
-      /** Bottom to top. */
+      /** Bottom to top; each pull request comes before the ones built on it. */
       numbers: Schema.Array(Schema.Int),
     }),
   ),

apps/web/src/components/pullRequest/pullRequestListLines.ts

@@ -4,7 +4,8 @@ import type { ThreadPullRequestChain } from "@t3tools/shared/threadPullRequests"
 /** One line of a thread's pull-request list: a link plus how deep it sits in its stack. */
 export interface PullRequestListLine {
   readonly link: ThreadPullRequestLink;
-  /** 0 for a pull request on the base branch; each layer above steps in by one. */
+  /** 0 for a pull request on the base branch; each layer above steps in by one. Pull requests
+   * built on the same parent share a depth. */
   readonly depth: number;
   /** Which chain the line belongs to, so callers can tell one stack's lines from another's. */
   readonly chainKey: string;
@@ -36,12 +37,12 @@ export function pullRequestListLines(
   );
   return ordered.flatMap((chain) => {
     const chainKey = chainKeyOf(chain);
-    return chain.layers.map((link, depth) => ({
+    return chain.layers.map((link, index) => ({
       link,
-      depth,
+      depth: chain.depths[index]!,
       chainKey,
       stack:
-        depth === 0 && chain.layers.length > 1
+        index === 0 && chain.layers.length > 1
           ? { kind: chain.kind, size: chain.layers.length }
           : null,
     }));

packages/shared/src/threadPullRequests.test.ts

@@ -270,6 +270,33 @@ describe("resolveThreadPullRequestChains", () => {
     ]);
   });
 
+  it("keeps every link built on the same parent under it", () => {
+    const links = [
+      link(3, { snapshot: snapshot({ headBranch: "c", baseBranch: "a" }) }),
+      link(5, { snapshot: snapshot({ headBranch: "p", baseBranch: "main" }) }),
+      link(6, { snapshot: snapshot({ headBranch: "q", baseBranch: "p" }) }),
+      link(1, { snapshot: snapshot({ headBranch: "a", baseBranch: "p" }) }),
+      link(2, { snapshot: snapshot({ headBranch: "b", baseBranch: "a" }) }),
+      link(9, { snapshot: snapshot({ headBranch: "solo", baseBranch: "main" }) }),
+    ];
+    const chains = resolveThreadPullRequestChains(links);
+    expect(
+      chains.map((chain) => [chain.layers.map((layer) => layer.number), chain.depths]),
+    ).toEqual([
+      // #6 and #1 both build on #5; #3 and #2 both build on #1.
+      [
+        [5, 6, 1, 3, 2],
+        [0, 1, 1, 2, 2],
+      ],
+      [[9], [0]],
+    ]);
+    expect(resolveThreadPullRequestBadge(links.slice(0, 5))).toEqual({
+      kind: "stack",
+      layers: 5,
+      state: "open",
+    });
+  });
+
   it("uses the native stack order when the host provides one", () => {
     const stack = {
       kind: "native" as const,

packages/shared/src/threadPullRequests.ts

@@ -204,14 +204,17 @@ export function legacyLinkedPullRequestOf(
 
 export interface ThreadPullRequestChain {
   readonly kind: "native" | "derived";
-  /** Bottom to top. */
+  /** Bottom to top. Each link comes before the links built on it. */
   readonly layers: ReadonlyArray<ThreadPullRequestLink>;
+  /** One per layer: 0 for the base, parent's depth + 1 above it. Siblings share a depth. */
+  readonly depths: ReadonlyArray<number>;
 }
 
 /**
  * Groups a thread's links into stacks. Native stacks come from the host and win; the rest
  * are chained by matching one link's base branch to another's head branch within the same
- * repository. A link that chains to nothing is a one-layer chain.
+ * repository. Several links can build on one parent, so a derived stack is a tree, listed
+ * depth first. A link that chains to nothing is a one-layer chain.
  */
 export function resolveThreadPullRequestChains(
   links: ReadonlyArray<ThreadPullRequestLink>,
@@ -233,7 +236,7 @@ export function resolveThreadPullRequestChains(
     const order = new Map(members[0]!.stack!.layers.map((layer, index) => [layer.number, index]));
     members.sort((left, right) => (order.get(left.number) ?? 0) - (order.get(right.number) ?? 0));
     for (const member of members) placed.add(threadPullRequestKeyOf(member));
-    chains.push({ kind: "native", layers: members });
+    chains.push({ kind: "native", layers: members, depths: members.map((_, index) => index) });
   }
 
   const remaining = visible.filter((link) => !placed.has(threadPullRequestKeyOf(link)));
@@ -248,31 +251,45 @@ export function resolveThreadPullRequestChains(
     const key = branchKey(link, link.snapshot.headBranch);
     byHead.set(key, byHead.has(key) ? null : link);
   }
-  const hasChild = new Set<string>();
-  for (const link of remaining) {
-    if (link.snapshot === null) continue;
+  const parentOf = (link: ThreadPullRequestLink) => {
+    if (link.snapshot === null) return undefined;
     const parent = byHead.get(branchKey(link, link.snapshot.baseBranch));
-    if (parent != null && parent !== link) hasChild.add(threadPullRequestKeyOf(parent));
+    return parent == null || parent === link ? undefined : parent;
+  };
+  const children = new Map<string, Array<ThreadPullRequestLink>>();
+  for (const link of remaining) {
+    const parent = parentOf(link);
+    if (parent === undefined) continue;
+    const key = threadPullRequestKeyOf(parent);
+    const siblings = children.get(key) ?? [];
+    siblings.push(link);
+    children.set(key, siblings);
   }
-  // Walk from each top (a link nothing builds on) down its base chain.
-  for (const top of remaining) {
-    if (hasChild.has(threadPullRequestKeyOf(top))) continue;
+  // Walk each base (a link that builds on no other link) depth first, so every link a
+  // parent has sits under it instead of only the first one.
+  for (const base of remaining) {
+    if (parentOf(base) !== undefined) continue;
     const layers: Array<ThreadPullRequestLink> = [];
-    let cursor: ThreadPullRequestLink | undefined = top;
-    while (cursor !== undefined && !placed.has(threadPullRequestKeyOf(cursor))) {
-      placed.add(threadPullRequestKeyOf(cursor));
-      layers.unshift(cursor);
-      cursor =
-        cursor.snapshot === null
-          ? undefined
-          : (byHead.get(branchKey(cursor, cursor.snapshot.baseBranch)) ?? undefined);
+    const depths: Array<number> = [];
+    const pending: Array<{ readonly link: ThreadPullRequestLink; readonly depth: number }> = [
+      { link: base, depth: 0 },
+    ];
+    for (let next = pending.pop(); next !== undefined; next = pending.pop()) {
+      const key = threadPullRequestKeyOf(next.link);
+      placed.add(key);
+      layers.push(next.link);
+      depths.push(next.depth);
+      const below = children.get(key) ?? [];
+      for (let index = below.length - 1; index >= 0; index -= 1) {
+        pending.push({ link: below[index]!, depth: next.depth + 1 });
+      }
     }
-    if (layers.length > 0) chains.push({ kind: "derived", layers });
+    chains.push({ kind: "derived", layers, depths });
   }
-  // Cycles have no top. Keep those links visible without inventing a stack order.
+  // Cycles have no base. Keep those links visible without inventing a stack order.
   for (const link of remaining) {
     if (!placed.has(threadPullRequestKeyOf(link))) {
-      chains.push({ kind: "derived", layers: [link] });
+      chains.push({ kind: "derived", layers: [link], depths: [0] });
     }
   }
   return chains;