diff --git a/actions/setup/js/safe_outputs_handlers.cjs b/actions/setup/js/safe_outputs_handlers.cjs
index b82062853ba..da0c183bcfe 100644
--- a/actions/setup/js/safe_outputs_handlers.cjs
+++ b/actions/setup/js/safe_outputs_handlers.cjs
@@ -1084,7 +1084,14 @@ function createHandlers(server, appendSafeOutput, config = {}) {
       server.debug(`Using configured patch_workspace_path for push_to_pull_request_branch: ${pushPatchWorkspacePath} -> ${repoCwd}`);
     }
 
-    if (((entry.repo && entry.repo.trim()) || pushConfig["target-repo"]) && !repoCwd) {
+    const envTargetSlug = (process.env.GH_AW_TARGET_REPO_SLUG || "").trim();
+    const currentRepo = (process.env.GITHUB_REPOSITORY || "").toLowerCase();
+    const envSlugIsSideRepo = envTargetSlug && envTargetSlug.toLowerCase() !== currentRepo;
+    if (envTargetSlug && !envSlugIsSideRepo) {
+      server.debug(`GH_AW_TARGET_REPO_SLUG (${envTargetSlug}) matches current repo; not using as side-repo checkout hint for push_to_pull_request_branch`);
+    }
+    const hasExplicitTargetRepoHint = (entry.repo && entry.repo.trim()) || pushConfig["target-repo"] || envSlugIsSideRepo;
+    if (hasExplicitTargetRepoHint && !repoCwd) {
       server.debug(`Looking for checkout of target repo: ${itemRepo}`);
       const checkoutResult = findRepoCheckout(itemRepo);
       if (!checkoutResult.success) {
diff --git a/actions/setup/js/safe_outputs_handlers.test.cjs b/actions/setup/js/safe_outputs_handlers.test.cjs
index cb987cd142d..a444d4d71c4 100644
--- a/actions/setup/js/safe_outputs_handlers.test.cjs
+++ b/actions/setup/js/safe_outputs_handlers.test.cjs
@@ -1551,6 +1551,37 @@ describe("safe_outputs_handlers", () => {
       }
     });
 
+    it("should detect branch from GH_AW_TARGET_REPO_SLUG checkout when target-repo is not configured", async () => {
+      const { targetRepoDir } = createSideRepoWithTrackedAndLocalCommits();
+      process.env.GH_AW_TARGET_REPO_SLUG = "test-owner/test-repo";
+      process.env.GITHUB_BASE_REF = "main";
+      execSync("git init -b main", { cwd: testWorkspaceDir, stdio: "pipe" });
+      execSync("git config user.email 'test@example.com'", { cwd: testWorkspaceDir, stdio: "pipe" });
+      execSync("git config user.name 'Test User'", { cwd: testWorkspaceDir, stdio: "pipe" });
+      fs.writeFileSync(path.join(testWorkspaceDir, "HOST.md"), "host\n");
+      execSync("git add HOST.md", { cwd: testWorkspaceDir, stdio: "pipe" });
+      execSync("git commit -m 'host base commit'", { cwd: testWorkspaceDir, stdio: "pipe" });
+      execSync("git remote add origin https://github.com/owner/repo.git", { cwd: testWorkspaceDir, stdio: "pipe" });
+
+      try {
+        const result = await handlers.pushToPullRequestBranchHandler({});
+
+        expect(result.isError).toBeFalsy();
+        expect(mockServer.debug).toHaveBeenCalledWith(expect.stringContaining(`Selected checkout folder for test-owner/test-repo: ${targetRepoDir}`));
+        expect(mockServer.debug).toHaveBeenCalledWith(expect.stringContaining("Using current branch for push_to_pull_request_branch: feature/test-change"));
+        expect(mockAppendSafeOutput).toHaveBeenCalledWith(
+          expect.objectContaining({
+            type: "push_to_pull_request_branch",
+            branch: "feature/test-change",
+            repo_cwd: targetRepoDir,
+          })
+        );
+      } finally {
+        delete process.env.GH_AW_TARGET_REPO_SLUG;
+        delete process.env.GITHUB_BASE_REF;
+      }
+    });
+
     it("should reject push_to_pull_request_branch when branch still equals base_branch after detection", async () => {
       // Simulates the scenario where getBaseBranch() incorrectly resolves to the
       // feature branch itself. Detection cannot recover when getCurrentBranch()
diff --git a/docs/src/content/docs/specs/checkout-behavior-specification.md b/docs/src/content/docs/specs/checkout-behavior-specification.md
index 7566c24dddb..abc0c41c560 100644
--- a/docs/src/content/docs/specs/checkout-behavior-specification.md
+++ b/docs/src/content/docs/specs/checkout-behavior-specification.md
@@ -7,7 +7,7 @@ sidebar:
 
 # Checkout Behavior Specification
 
-**Version**: 1.0.0  
+**Version**: 1.1.0  
 **Status**: Working Draft  
 **Publication Date**: 2026-07-08  
 **Editor**: GitHub Agentic Workflows Team  
@@ -230,6 +230,22 @@ Effective side-repo token precedence MUST be:
 2. side-repo target checkout `github-app` minted token reference
 3. `${{ secrets.GH_AW_GITHUB_TOKEN }}`
 
+### 6.3 `push_to_pull_request_branch` Side-Repo Checkout Resolution
+
+The `push_to_pull_request_branch` safe-output handler MUST resolve the target checkout directory from one of three sources, evaluated in priority order:
+
+1. `patch_workspace_path` configuration (explicit path; resolved via `resolvePatchWorkspacePath`).
+2. `entry.repo` field or `target-repo` workflow config entry — triggers `findRepoCheckout` lookup.
+3. `GH_AW_TARGET_REPO_SLUG` environment variable — used as a side-repo checkout hint **only when** its value (case-insensitively) differs from `GITHUB_REPOSITORY`. When the env var is set but matches `GITHUB_REPOSITORY`, it MUST be ignored and the handler MUST log a debug message explaining the passthrough.
+
+When source 2 or 3 triggers a `findRepoCheckout` lookup, all subsequent git operations for that handler invocation (branch detection, patch generation, bundle generation) MUST operate under the resolved checkout directory (`repo_cwd`) rather than the workspace root.
+
+When `GH_AW_TARGET_REPO_SLUG` is used as a side-repo hint (source 3), the implementation SHOULD emit an informational debug log identifying the resolved `owner/repo`.
+
+When `GH_AW_TARGET_REPO_SLUG` is set but equals `GITHUB_REPOSITORY`, the implementation MUST emit a debug log stating that the variable is not being used as a side-repo hint and explaining why.
+
+**Rationale**: `GH_AW_TARGET_REPO_SLUG` may be globally set in side-repo maintenance workflows for cross-repo operations other than `push_to_pull_request_branch`. Using it unconditionally as a checkout hint would misdirect branch and patch detection when the push target is the current (workflow-host) repository.
+
 ---
 
 ## 7. Compliance Testing
@@ -250,6 +266,7 @@ Effective side-repo token precedence MUST be:
 - **T-CHK-012**: safe_outputs checkout token MUST NOT use `safe-outputs.github-app` or `safe-outputs.github-token`; only `safe-outputs-github-app` (per entry) or `GITHUB_TOKEN` are permitted
 - **T-CHK-013**: Checkout-manifest generation includes safe_outputs auth metadata without persisting resolved tokens
 - **T-CHK-014**: Checkout-manifest path resolution MUST reject paths that are absolute (e.g., `/etc/passwd`) or escape the workspace root (e.g., `../../sensitive`); rejected paths MUST produce an error and MUST NOT be used for checkout or file lookup
+- **T-CHK-015**: `push_to_pull_request_branch` uses side-repo checkout from `GH_AW_TARGET_REPO_SLUG` only when it differs from `GITHUB_REPOSITORY`; emits debug log and ignores it when they match
 
 ### 7.2 Compliance Checklist
 
@@ -264,6 +281,7 @@ Effective side-repo token precedence MUST be:
 | Checkout-level safe_outputs auth field | T-CHK-011, T-CHK-012 | C1/C2 | Required |
 | Checkout-manifest generation requirements | T-CHK-013 | C1/C2 | Required |
 | Checkout-manifest path-escape rejection | T-CHK-014 | C2 | Required |
+| `push_to_pull_request_branch` side-repo cwd resolution | T-CHK-015 | C2 | Required |
 
 ### 7.3 Safeguards
 
@@ -305,6 +323,11 @@ The following MUST-level norms govern credential and token safety during checkou
 
 ## 9. Change Log
 
+### Version 1.1.0 (Working Draft)
+
+- Added §6.3: `push_to_pull_request_branch` side-repo checkout resolution requirements, covering `GH_AW_TARGET_REPO_SLUG` passthrough guard, debug-logging obligation, and `repo_cwd` scoping of all git operations.
+- Added T-CHK-015 to §7.1 and §7.2 compliance checklist.
+
 ### Version 1.0.0 (Working Draft)
 
 - Initial specification for checkout behavior in activation, agent, and safe_outputs jobs