diff --git a/actions/setup/js/safe_outputs_tools.json b/actions/setup/js/safe_outputs_tools.json
index f4da663e56e..d8acf2197a9 100644
--- a/actions/setup/js/safe_outputs_tools.json
+++ b/actions/setup/js/safe_outputs_tools.json
@@ -1008,6 +1008,11 @@
           "type": ["number", "string"],
           "description": "Issue or pull request number to add to the project. This is the numeric ID from the GitHub URL (e.g., 123 in github.com/owner/repo/issues/123 for issue #123, or 456 in github.com/owner/repo/pull/456 for PR #456), or a temporary ID from a recent create_issue call (e.g., 'aw_abc123', '#aw_Test123'). Required when content_type is 'issue' or 'pull_request'."
         },
+        "content_repo": {
+          "type": "string",
+          "pattern": "^[A-Za-z0-9_.-]+/[A-Za-z0-9_.-]+$",
+          "description": "Repository that owns the issue or PR, in 'owner/repo' format (e.g., 'github/docs'). When provided, overrides the workflow host repository for resolving content_number. Use this for cross-repo project item resolution when the issue/PR lives in a different repository than where the workflow runs."
+        },
         "draft_title": {
           "type": "string",
           "description": "Title for a Projects v2 draft issue. Required when content_type is 'draft_issue' and creating a new draft (when draft_issue_id is not provided)."
diff --git a/actions/setup/js/update_project.cjs b/actions/setup/js/update_project.cjs
index 638083f2bfd..64599e2bf24 100644
--- a/actions/setup/js/update_project.cjs
+++ b/actions/setup/js/update_project.cjs
@@ -23,6 +23,9 @@ function normalizeUpdateProjectOutput(value) {
 
   if (output.content_type === undefined && output.contentType !== undefined) output.content_type = output.contentType;
   if (output.content_number === undefined && output.contentNumber !== undefined) output.content_number = output.contentNumber;
+  if (output.content_repo === undefined && output.contentRepo !== undefined) output.content_repo = output.contentRepo;
+  // Support YAML dash-style alias: content-repo → content_repo
+  if (output.content_repo === undefined && output["content-repo"] !== undefined) output.content_repo = output["content-repo"];
 
   if (output.draft_title === undefined && output.draftTitle !== undefined) output.draft_title = output.draftTitle;
   if (output.draft_body === undefined && output.draftBody !== undefined) output.draft_body = output.draftBody;
@@ -1009,12 +1012,26 @@ async function updateProject(output, temporaryIdMap = new Map(), githubClient =
       }
     }
     if (null !== contentNumber) {
+      // Determine owner/repo for content resolution: content_repo overrides context.repo for cross-repo support
+      let contentOwner = owner;
+      let contentRepo = repo;
+      if (output.content_repo) {
+        const trimmedContentRepo = output.content_repo.trim();
+        const parts = trimmedContentRepo.split("/").map(p => p.trim());
+        if (parts.length === 2 && parts[0] && parts[1]) {
+          contentOwner = parts[0];
+          contentRepo = parts[1];
+          core.info(`Using content_repo for resolution: ${contentOwner}/${contentRepo}`);
+        } else {
+          core.warning(`Invalid content_repo format "${output.content_repo}": expected "owner/repo". Falling back to workflow host repository.`);
+        }
+      }
       const contentType = "pull_request" === output.content_type ? "PullRequest" : "issue" === output.content_type || output.issue ? "Issue" : "PullRequest",
         contentQuery =
           "Issue" === contentType
             ? "query($owner: String!, $repo: String!, $number: Int!) {\n            repository(owner: $owner, name: $repo) {\n              issue(number: $number) {\n                id\n              }\n            }\n          }"
             : "query($owner: String!, $repo: String!, $number: Int!) {\n            repository(owner: $owner, name: $repo) {\n              pullRequest(number: $number) {\n                id\n              }\n            }\n          }",
-        contentResult = await github.graphql(contentQuery, { owner, repo, number: contentNumber }),
+        contentResult = await github.graphql(contentQuery, { owner: contentOwner, repo: contentRepo, number: contentNumber }),
         contentData = "Issue" === contentType ? contentResult.repository.issue : contentResult.repository.pullRequest,
         contentId = contentData.id,
         existingItem = await (async function (projectId, contentId) {
diff --git a/actions/setup/js/update_project.test.cjs b/actions/setup/js/update_project.test.cjs
index 62f71b539b5..b10188ee19c 100644
--- a/actions/setup/js/update_project.test.cjs
+++ b/actions/setup/js/update_project.test.cjs
@@ -1015,6 +1015,140 @@ describe("updateProject", () => {
     await expect(updateProject(output, temporaryIdMap)).rejects.toThrow(/Temporary ID 'aw_abc789' not found in map/);
   });
 
+  it("resolves content_number using content_repo for cross-repo issues", async () => {
+    const projectUrl = "https://github.com/orgs/testowner/projects/60";
+    const output = {
+      type: "update_project",
+      project: projectUrl,
+      content_type: "issue",
+      content_number: 99,
+      content_repo: "otherowner/otherrepo",
+    };
+
+    queueResponses([repoResponse(), viewerResponse(), orgProjectV2Response(projectUrl, 60, "project-cross-repo"), issueResponse("cross-repo-issue-id"), emptyItemsResponse(), { addProjectV2ItemById: { item: { id: "cross-repo-item" } } }]);
+
+    await updateProject(output);
+
+    // Verify the content resolution used the cross-repo owner/repo
+    const contentQuery = mockGithub.graphql.mock.calls.find(([query, vars]) => query.includes("issue(number:") && vars?.owner === "otherowner");
+    expect(contentQuery).toBeDefined();
+    expect(contentQuery[1]).toMatchObject({ owner: "otherowner", repo: "otherrepo", number: 99 });
+    expect(mockCore.info).toHaveBeenCalledWith(expect.stringContaining("Using content_repo for resolution: otherowner/otherrepo"));
+    expect(getOutput("item-id")).toBe("cross-repo-item");
+  });
+
+  it("resolves content_number using content_repo for cross-repo pull requests", async () => {
+    const projectUrl = "https://github.com/orgs/testowner/projects/60";
+    const output = {
+      type: "update_project",
+      project: projectUrl,
+      content_type: "pull_request",
+      content_number: 55,
+      content_repo: "anotherorg/anotherrepo",
+    };
+
+    queueResponses([
+      repoResponse(),
+      viewerResponse(),
+      orgProjectV2Response(projectUrl, 60, "project-cross-repo-pr"),
+      pullRequestResponse("cross-repo-pr-id"),
+      emptyItemsResponse(),
+      { addProjectV2ItemById: { item: { id: "cross-repo-pr-item" } } },
+    ]);
+
+    await updateProject(output);
+
+    // Verify the content resolution used the cross-repo owner/repo
+    const prQuery = mockGithub.graphql.mock.calls.find(([query, vars]) => query.includes("pullRequest(number:") && vars?.owner === "anotherorg");
+    expect(prQuery).toBeDefined();
+    expect(prQuery[1]).toMatchObject({ owner: "anotherorg", repo: "anotherrepo", number: 55 });
+    expect(getOutput("item-id")).toBe("cross-repo-pr-item");
+  });
+
+  it("normalizes camelCase contentRepo to content_repo", async () => {
+    const projectUrl = "https://github.com/orgs/testowner/projects/60";
+    const output = {
+      type: "update_project",
+      project: projectUrl,
+      content_type: "issue",
+      content_number: 77,
+      contentRepo: "camelowner/camelrepo",
+    };
+
+    queueResponses([repoResponse(), viewerResponse(), orgProjectV2Response(projectUrl, 60, "project-camel-repo"), issueResponse("camel-issue-id"), emptyItemsResponse(), { addProjectV2ItemById: { item: { id: "camel-item" } } }]);
+
+    await updateProject(output);
+
+    const contentQuery = mockGithub.graphql.mock.calls.find(([query, vars]) => query.includes("issue(number:") && vars?.owner === "camelowner");
+    expect(contentQuery).toBeDefined();
+    expect(contentQuery[1]).toMatchObject({ owner: "camelowner", repo: "camelrepo", number: 77 });
+    expect(getOutput("item-id")).toBe("camel-item");
+  });
+
+  it("normalizes dash-style content-repo alias to content_repo", async () => {
+    const projectUrl = "https://github.com/orgs/testowner/projects/60";
+    const output = {
+      type: "update_project",
+      project: projectUrl,
+      content_type: "issue",
+      content_number: 88,
+      "content-repo": "dashowner/dashrepo",
+    };
+
+    queueResponses([repoResponse(), viewerResponse(), orgProjectV2Response(projectUrl, 60, "project-dash-repo"), issueResponse("dash-issue-id"), emptyItemsResponse(), { addProjectV2ItemById: { item: { id: "dash-item" } } }]);
+
+    await updateProject(output);
+
+    const contentQuery = mockGithub.graphql.mock.calls.find(([query, vars]) => query.includes("issue(number:") && vars?.owner === "dashowner");
+    expect(contentQuery).toBeDefined();
+    expect(contentQuery[1]).toMatchObject({ owner: "dashowner", repo: "dashrepo", number: 88 });
+    expect(getOutput("item-id")).toBe("dash-item");
+  });
+
+  it("trims whitespace from content_repo before resolving", async () => {
+    const projectUrl = "https://github.com/orgs/testowner/projects/60";
+    const output = {
+      type: "update_project",
+      project: projectUrl,
+      content_type: "issue",
+      content_number: 99,
+      content_repo: "  trimowner/trimrepo  ",
+    };
+
+    queueResponses([repoResponse(), viewerResponse(), orgProjectV2Response(projectUrl, 60, "project-trim-repo"), issueResponse("trim-issue-id"), emptyItemsResponse(), { addProjectV2ItemById: { item: { id: "trim-item" } } }]);
+
+    await updateProject(output);
+
+    const contentQuery = mockGithub.graphql.mock.calls.find(([query, vars]) => query.includes("issue(number:") && vars?.owner === "trimowner");
+    expect(contentQuery).toBeDefined();
+    expect(contentQuery[1]).toMatchObject({ owner: "trimowner", repo: "trimrepo", number: 99 });
+    expect(mockCore.warning).not.toHaveBeenCalled();
+  });
+
+  it("warns and falls back to context.repo on invalid content_repo format (no slash)", async () => {
+    const projectUrl = "https://github.com/orgs/testowner/projects/60";
+    const output = {
+      type: "update_project",
+      project: projectUrl,
+      content_type: "issue",
+      content_number: 42,
+      content_repo: "noslashrepo",
+    };
+
+    queueResponses([repoResponse(), viewerResponse(), orgProjectV2Response(projectUrl, 60, "project-fallback"), issueResponse("fallback-issue-id"), emptyItemsResponse(), { addProjectV2ItemById: { item: { id: "fallback-item" } } }]);
+
+    await updateProject(output);
+
+    // Warning should be emitted once with the full invalid format message
+    expect(mockCore.warning).toHaveBeenCalledTimes(1);
+    expect(mockCore.warning).toHaveBeenCalledWith(expect.stringContaining('Invalid content_repo format "noslashrepo": expected "owner/repo". Falling back to workflow host repository.'));
+
+    // GraphQL content query should use context.repo fallback (testowner/testrepo)
+    const contentQuery = mockGithub.graphql.mock.calls.find(([query, vars]) => query.includes("issue(number:") && vars?.owner === "testowner" && vars?.repo === "testrepo");
+    expect(contentQuery).toBeDefined();
+    expect(contentQuery[1]).toMatchObject({ owner: "testowner", repo: "testrepo", number: 42 });
+  });
+
   it("updates an existing text field", async () => {
     const projectUrl = "https://github.com/orgs/testowner/projects/60";
     const output = {
diff --git a/pkg/workflow/js/safe_outputs_tools.json b/pkg/workflow/js/safe_outputs_tools.json
index 55537e67542..6a58c97ef48 100644
--- a/pkg/workflow/js/safe_outputs_tools.json
+++ b/pkg/workflow/js/safe_outputs_tools.json
@@ -1222,6 +1222,11 @@
           ],
           "description": "Issue or pull request number to add to the project. This is the numeric ID from the GitHub URL (e.g., 123 in github.com/owner/repo/issues/123 for issue #123, or 456 in github.com/owner/repo/pull/456 for PR #456), or a temporary ID from a recent create_issue call (e.g., 'aw_abc123', '#aw_Test123'). Required when content_type is 'issue' or 'pull_request'."
         },
+        "content_repo": {
+          "type": "string",
+          "pattern": "^[A-Za-z0-9_.-]+/[A-Za-z0-9_.-]+$",
+          "description": "Repository that owns the issue or PR, in 'owner/repo' format (e.g., 'github/docs'). When provided, overrides the workflow host repository for resolving content_number. Use this for cross-repo project item resolution when the issue/PR lives in a different repository than where the workflow runs."
+        },
         "draft_title": {
           "type": "string",
           "description": "Title for a Projects v2 draft issue. Required when content_type is 'draft_issue'."
diff --git a/schemas/agent-output.json b/schemas/agent-output.json
index 1602dd7fb9f..1a78c3ca3c1 100644
--- a/schemas/agent-output.json
+++ b/schemas/agent-output.json
@@ -593,6 +593,10 @@
           "oneOf": [{ "type": "number" }, { "type": "string" }],
           "description": "Issue or PR number (preferred field)"
         },
+        "content_repo": {
+          "type": "string",
+          "description": "Repository that owns the issue or PR, in 'owner/repo' format (e.g., 'github/docs'). When provided, overrides the workflow host repository for resolving content_number. Use this for cross-repo project item resolution when the issue/PR lives in a different repository than where the workflow runs."
+        },
         "issue": {
           "oneOf": [{ "type": "number" }, { "type": "string" }],
           "description": "Issue number (legacy field, use content_number instead)"