ci: skip Claude-backed test jobs on fork PRs (#1655)

* ci: skip Claude-backed test jobs on fork PRs

Jobs that run the action against the Claude API authenticate via workload
identity federation, which fork PRs cannot mint an OIDC token for, so they
always failed on external contributions. Gate each such job on the PR head
repo matching the base repo; push and workflow_dispatch runs are unaffected.

No-Verification-Needed: CI workflow config only, exercised by Actions on the PR

* test: pin the bare remote's initial branch in fetch-depth test

The shallow-clone case created its bare remote with a plain git init, so
HEAD pointed at whatever init.defaultBranch resolves to (master on CI)
while the test only pushed main. git clone --depth=1 implies
--single-branch, and with a dangling remote HEAD it produces an empty,
non-shallow clone, so the is-shallow assertion failed on runners whose
default branch is not main.

No-Verification-Needed: test-only change

.github/workflows/test-structured-output.yml

@@ -15,6 +15,8 @@ permissions:
 jobs:
   test-basic-types:
     name: Test Basic Type Conversions
+    # Skip on fork PRs since they can't mint the OIDC token used for Claude API auth
+    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -76,6 +78,8 @@ jobs:
 
   test-complex-types:
     name: Test Arrays and Objects
+    # Skip on fork PRs since they can't mint the OIDC token used for Claude API auth
+    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -129,6 +133,8 @@ jobs:
 
   test-edge-cases:
     name: Test Edge Cases
+    # Skip on fork PRs since they can't mint the OIDC token used for Claude API auth
+    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -190,6 +196,8 @@ jobs:
 
   test-name-sanitization:
     name: Test Output Name Sanitization
+    # Skip on fork PRs since they can't mint the OIDC token used for Claude API auth
+    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -232,6 +240,8 @@ jobs:
 
   test-execution-file-structure:
     name: Test Execution File Format
+    # Skip on fork PRs since they can't mint the OIDC token used for Claude API auth
+    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -284,7 +294,7 @@ jobs:
       - test-edge-cases
       - test-name-sanitization
       - test-execution-file-structure
-    if: always()
+    if: ${{ always() && (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository) }}
     steps:
       - name: Generate Summary
         run: |