diff --git a/apps/server/src/pullRequest/GitHubPullRequestCli.ts b/apps/server/src/pullRequest/GitHubPullRequestCli.ts
index 4faaba2c66cf..f51cc4c3997a 100644
--- a/apps/server/src/pullRequest/GitHubPullRequestCli.ts
+++ b/apps/server/src/pullRequest/GitHubPullRequestCli.ts
@@ -91,6 +91,7 @@ import {
   type GitHubReviewThreadPage,
   type GitHubViewerAccess,
 } from "./gitHubPullRequestJson.ts";
+import { makeGitHubNativeStackRead } from "./gitHubNativeStack.ts";
 import type { ProviderListCursor } from "./PullRequestProvider.ts";
 
 /**
@@ -407,6 +408,8 @@ export interface GitHubPullRequestDiffSlice {
 export class GitHubPullRequestCli extends Context.Service<
   GitHubPullRequestCli,
   {
+    readonly getNativeDependencyMembership: ReturnType<typeof makeGitHubNativeStackRead>;
+
     readonly getViewerLogin: (input: {
       readonly cwd: string;
     }) => Effect.Effect<string, GitHubPullRequestCliError>;
@@ -1460,6 +1463,7 @@ export const make = Effect.gen(function* () {
         );
 
   return GitHubPullRequestCli.of({
+    getNativeDependencyMembership: makeGitHubNativeStackRead(github.execute),
     getViewerLogin: (input) =>
       github.execute({ cwd: input.cwd, args: ["api", "user", "--jq", ".login"] }).pipe(
         Effect.flatMap((result) => {
diff --git a/apps/server/src/pullRequest/GitHubPullRequestProvider.ts b/apps/server/src/pullRequest/GitHubPullRequestProvider.ts
index b700e554b4ce..7c18658116b1 100644
--- a/apps/server/src/pullRequest/GitHubPullRequestProvider.ts
+++ b/apps/server/src/pullRequest/GitHubPullRequestProvider.ts
@@ -210,6 +210,8 @@ export const make = Effect.gen(function* () {
     kind: "github",
     capabilities: CAPABILITIES,
 
+    getNativeDependencyMembership: (input) => cli.getNativeDependencyMembership(input),
+
     getViewer: (input) =>
       cli.getViewerLogin({ cwd: input.cwd }).pipe(Effect.mapError(fail("getViewer"))),
 
diff --git a/apps/server/src/pullRequest/gitHubNativeStack.test.ts b/apps/server/src/pullRequest/gitHubNativeStack.test.ts
new file mode 100644
index 000000000000..feb95f2fdc43
--- /dev/null
+++ b/apps/server/src/pullRequest/gitHubNativeStack.test.ts
@@ -0,0 +1,135 @@
+import { expect, it } from "@effect/vitest";
+import * as Effect from "effect/Effect";
+import * as Result from "effect/Result";
+import * as Schema from "effect/Schema";
+import { ChildProcessSpawner } from "effect/unstable/process";
+
+import { makeGitHubNativeStackRead } from "./gitHubNativeStack.ts";
+
+const input = { cwd: "/w", repository: "acme/web", host: "github.com", number: 2, limit: 100 };
+const repo = { url: "https://api.github.com/repos/acme/web" };
+const member = (number: number) => ({
+  number,
+  title: `Change ${number}`,
+  html_url: `https://github.com/acme/web/pull/${number}`,
+  state: "open",
+  draft: false,
+  merged_at: null as string | null,
+  head: { ref: `branch-${number}`, repo },
+  base: { ref: number === 1 ? "main" : `branch-${number - 1}`, repo },
+});
+const stack = (members = [member(1), member(2)]) => ({
+  number: 6,
+  node_id: "PRS_6",
+  pull_requests: members,
+});
+function fixture(responses: ReadonlyArray<unknown>, truncated = false) {
+  const encode = Schema.encodeSync(Schema.fromJsonString(Schema.Unknown));
+  const encoded = responses.map((response) => encode(response));
+  const requests: ReadonlyArray<string>[] = [];
+  const read = makeGitHubNativeStackRead((request) =>
+    Effect.sync(() => {
+      requests.push(request.args);
+      return {
+        exitCode: ChildProcessSpawner.ExitCode(0),
+        stdout: encoded[requests.length - 1] ?? "",
+        stderr: "",
+        stdoutTruncated: truncated,
+        stderrTruncated: false,
+        stdoutInvalidUtf8: false,
+      };
+    }),
+  );
+  return { read, requests };
+}
+
+it.effect(
+  "reads an exact membership and preserves merged roots with qualified source identity",
+  () =>
+    Effect.gen(function* () {
+      const root = { ...member(1), state: "closed", merged_at: "2026-09-01T00:00:00Z" };
+      const { read, requests } = fixture([[{ number: 6 }], stack([root, member(2)])]);
+      const result = yield* read(input);
+      expect(requests).toHaveLength(2);
+      expect(requests[0]).toContain("repos/acme/web/stacks?pull_request=2&per_page=2&page=1");
+      expect(result.status).toBe("present");
+      if (result.status !== "present") return;
+      expect(
+        result.members.map((pr) => [pr.number, pr.state, pr.headRepositoryNameWithOwner]),
+      ).toEqual([
+        [1, "merged", "acme/web"],
+        [2, "open", "acme/web"],
+      ]);
+      expect(result.coverage).toBe("complete");
+    }),
+);
+
+it.effect("only a successful empty exact lookup establishes no native stack", () =>
+  Effect.gen(function* () {
+    const { read, requests } = fixture([[]]);
+    expect(yield* read(input)).toEqual({ status: "none" });
+    expect(requests).toHaveLength(1);
+    const broken = fixture([[{ number: 6 }]], true);
+    expect(Result.isFailure(yield* Effect.result(broken.read(input)))).toBe(true);
+  }),
+);
+
+it.effect("bounds native membership while retaining the selected member", () =>
+  Effect.gen(function* () {
+    const { read } = fixture([[{ number: 6 }], stack([member(1), member(2), member(3)])]);
+    const result = yield* read({ ...input, number: 3, limit: 2 });
+    expect(result.status).toBe("present");
+    if (result.status !== "present") return;
+    expect(result.members.map((pr) => pr.number)).toEqual([2, 3]);
+    expect(result.coverage).toBe("partial");
+  }),
+);
+
+it.effect(
+  "rejects mismatched repositories, duplicate members, missing focus and ambiguous membership",
+  () =>
+    Effect.gen(function* () {
+      const foreign = {
+        ...member(2),
+        base: { ref: "main", repo: { url: "https://api.github.com/repos/other/web" } },
+      };
+      for (const responses of [
+        [[{ number: 6 }], stack([member(1), foreign])],
+        [[{ number: 6 }], stack([member(2), member(2)])],
+        [[{ number: 6 }], stack([member(1)])],
+        [[{ number: 6 }], stack([{ ...member(2), title: " " }])],
+        [[{ number: 6 }], { ...stack(), node_id: "" }],
+        [[{ number: 6 }, { number: 7 }]],
+      ]) {
+        const { read } = fixture(responses);
+        expect(Result.isFailure(yield* Effect.result(read(input)))).toBe(true);
+      }
+    }),
+);
+
+it.effect("does not infer source identity from membership or a different API host", () =>
+  Effect.gen(function* () {
+    const fork = {
+      ...member(1),
+      head: { ref: "branch-1", repo: { url: "https://api.github.com/repos/fork/web" } },
+    };
+    const unknown = {
+      ...member(2),
+      head: { ref: "branch-2", repo: { url: "https://other.example/repos/acme/web" } },
+    };
+    const { read } = fixture([[{ number: 6 }], stack([fork, unknown])]);
+    const result = yield* read(input);
+    if (result.status !== "present") return yield* Effect.die("expected native members");
+    expect(result.members.map((pr) => pr.headRepositoryNameWithOwner)).toEqual(["fork/web", null]);
+  }),
+);
+
+it.effect("leaves unverified enterprise hosts unavailable without an API request", () =>
+  Effect.gen(function* () {
+    const { read, requests } = fixture([]);
+    expect(Result.isFailure(yield* Effect.result(read({ ...input, host: "git.acme.test" })))).toBe(
+      true,
+    );
+    expect(requests).toHaveLength(0);
+  }),
+);
diff --git a/apps/server/src/pullRequest/gitHubNativeStack.ts b/apps/server/src/pullRequest/gitHubNativeStack.ts
new file mode 100644
index 000000000000..3983b63ba4ee
--- /dev/null
+++ b/apps/server/src/pullRequest/gitHubNativeStack.ts
@@ -0,0 +1,153 @@
+import * as Effect from "effect/Effect";
+import * as Result from "effect/Result";
+import * as Schema from "effect/Schema";
+import { TrimmedNonEmptyString } from "@t3tools/contracts";
+import { decodeJsonResult } from "@t3tools/shared/schemaJson";
+
+import type { GitHubCli } from "../sourceControl/GitHubCli.ts";
+import {
+  PullRequestProviderError,
+  type ProviderNativeDependencyMembership,
+  type ProviderRepositoryRef,
+} from "./PullRequestProvider.ts";
+
+const StackNumber = Schema.Int.check(Schema.isGreaterThan(0));
+const decodeList = decodeJsonResult(Schema.Array(Schema.Struct({ number: StackNumber })));
+const Repository = Schema.Struct({ url: Schema.String });
+const Branch = Schema.Struct({ ref: TrimmedNonEmptyString, repo: Schema.NullOr(Repository) });
+const decodeStack = decodeJsonResult(
+  Schema.Struct({
+    number: StackNumber,
+    node_id: TrimmedNonEmptyString,
+    pull_requests: Schema.Array(
+      Schema.Struct({
+        number: StackNumber,
+        title: TrimmedNonEmptyString,
+        html_url: TrimmedNonEmptyString,
+        state: Schema.Literals(["open", "closed"]),
+        draft: Schema.Boolean,
+        merged_at: Schema.NullOr(Schema.String),
+        head: Branch,
+        base: Branch,
+      }),
+    ),
+  }),
+);
+
+/** The preview embeds repository API URLs, not `full_name`. Never guess from a short name. */
+function repositoryIdentity(url: string | undefined): string | null {
+  if (url === undefined) return null;
+  try {
+    const parsed = new URL(url);
+    if (parsed.origin !== "https://api.github.com") return null;
+    return /^\/repos\/([^/]+\/[^/]+)\/?$/u.exec(parsed.pathname)?.[1] ?? null;
+  } catch {
+    return null;
+  }
+}
+
+/** Two bounded REST reads; a failed preview endpoint is unavailable, never an empty stack. */
+export const makeGitHubNativeStackRead = (execute: GitHubCli["Service"]["execute"]) =>
+  Effect.fn("GitHubNativeStack.read")(function* (
+    input: ProviderRepositoryRef & { readonly number: number; readonly limit: number },
+  ) {
+    const failed = (detail: string, cause?: unknown) =>
+      new PullRequestProviderError({
+        provider: "github",
+        operation: "getNativeDependencyMembership",
+        reason: "failed",
+        detail,
+        cause,
+      });
+    // GitHub Enterprise versions have not been verified against this public preview.
+    if (input.host.toLowerCase() !== "github.com") {
+      return yield* failed("Native stack membership is unavailable on this GitHub host.");
+    }
+    const repository = input.repository.split("/").map(encodeURIComponent).join("/");
+    const read = (path: string) =>
+      execute({
+        cwd: input.cwd,
+        args: [
+          "api",
+          "--hostname",
+          input.host,
+          "--method",
+          "GET",
+          "-H",
+          "Accept: application/vnd.github+json",
+          "-H",
+          "X-GitHub-Api-Version: 2026-03-10",
+          path,
+        ],
+        maxOutputBytes: 2 * 1024 * 1024,
+      }).pipe(
+        Effect.mapError(
+          (error) =>
+            new PullRequestProviderError({
+              provider: "github",
+              operation: "getNativeDependencyMembership",
+              reason:
+                error._tag === "GitHubCliRateLimitError"
+                  ? "rate-limited"
+                  : error._tag === "GitHubCliAuthenticationError"
+                    ? "unauthenticated"
+                    : error._tag === "GitHubCliUnavailableError"
+                      ? "missing-tool"
+                      : "failed",
+              detail: error.detail,
+              cause: error,
+            }),
+        ),
+        Effect.flatMap((output) =>
+          output.stdoutTruncated || output.stdoutInvalidUtf8
+            ? Effect.fail(failed("Native stack response exceeded the read limit."))
+            : Effect.succeed(output.stdout),
+        ),
+      );
+    // The exact membership filter returns at most one stack; two rows detect a broken answer.
+    const listed = decodeList(
+      yield* read(`repos/${repository}/stacks?pull_request=${input.number}&per_page=2&page=1`),
+    );
+    if (Result.isFailure(listed))
+      return yield* failed("Unreadable native stack listing.", listed.failure);
+    if (listed.success.length === 0)
+      return { status: "none" } satisfies ProviderNativeDependencyMembership;
+    if (listed.success.length !== 1) return yield* failed("Native stack membership was ambiguous.");
+    const stackNumber = listed.success[0]!.number;
+    const decoded = decodeStack(yield* read(`repos/${repository}/stacks/${stackNumber}`));
+    if (Result.isFailure(decoded))
+      return yield* failed("Unreadable native stack members.", decoded.failure);
+    const stack = decoded.success;
+    if (
+      stack.number !== stackNumber ||
+      !stack.pull_requests.some((pr) => pr.number === input.number) ||
+      new Set(stack.pull_requests.map((pr) => pr.number)).size !== stack.pull_requests.length ||
+      stack.pull_requests.some(
+        (pr) =>
+          repositoryIdentity(pr.base.repo?.url)?.toLowerCase() !== input.repository.toLowerCase(),
+      )
+    ) {
+      return yield* failed(
+        "Native stack members did not match the requested repository and pull request.",
+      );
+    }
+    const limit = Math.max(1, Math.min(input.limit, 100));
+    // Keep the selected member visible even if it is beyond the display budget.
+    const focusIndex = stack.pull_requests.findIndex((pr) => pr.number === input.number);
+    const start = Math.max(0, focusIndex - limit + 1);
+    return {
+      status: "present",
+      id: stack.node_id,
+      coverage: stack.pull_requests.length > limit ? "partial" : "complete",
+      members: stack.pull_requests.slice(start, start + limit).map((pr) => ({
+        number: pr.number,
+        title: pr.title,
+        url: pr.html_url,
+        state: pr.merged_at !== null ? "merged" : pr.state,
+        isDraft: pr.draft,
+        headBranch: pr.head.ref,
+        baseBranch: pr.base.ref,
+        headRepositoryNameWithOwner: repositoryIdentity(pr.head.repo?.url),
+      })),
+    } satisfies ProviderNativeDependencyMembership;
+  });