fix: treat empty ISSUE_NUMBER env as unset

A workflow that combines `on: issues` with `workflow_dispatch` will
typically set `ISSUE_NUMBER: ${{ github.event.inputs.issue_number }}`,
which evaluates to the empty string on the auto-trigger. The old check
`"ISSUE_NUMBER" in os.environ` then took the env-var branch and crashed
in int("").

Read with os.environ.get(..., "").strip() so empty/whitespace falls
through to the event payload, where auto-detection already works.

Update the README example to show the combined auto+manual trigger
pattern and the matching ISSUE_NUMBER fallback so consumers copy the
safe form. Add a regression test for the empty-string case and
simplify the existing event-file test now that the workaround is no
longer needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Douglas Blank

README.md

@@ -41,10 +41,16 @@ name: Scout Issue Triage
 on:
   issues:
     types: [opened]
+  workflow_dispatch:
+    inputs:
+      issue_number:
+        description: Issue number to triage
+        required: true
+        type: number
 
 # One Scout run per issue at a time
 concurrency:
-  group: scout-issue-${{ github.event.issue.number }}
+  group: scout-issue-${{ github.event.issue.number || github.event.inputs.issue_number }}
   cancel-in-progress: false
 
 jobs:
@@ -67,6 +73,7 @@ jobs:
           SCOUT_GITHUB_REPO_NAME: ${{ vars.SCOUT_GITHUB_REPO_NAME }}
           OPIK_API_KEY: ${{ secrets.OPIK_API_KEY }}
           OPIK_WORKSPACE: ${{ vars.OPIK_WORKSPACE }}
+          ISSUE_NUMBER: ${{ github.event.issue.number || github.event.inputs.issue_number }}
 ```
 
 ## GitHub App requirements

scout.py

@@ -60,8 +60,11 @@ def _get_repo_owner_name() -> tuple[str, str]:
 
 def _get_issue_number() -> int:
     """Resolve issue number from ISSUE_NUMBER or the GitHub Actions event payload."""
-    if "ISSUE_NUMBER" in os.environ:
-        return int(os.environ["ISSUE_NUMBER"])
+    # Treat empty as unset: workflows often pass `${{ github.event.inputs.foo }}`,
+    # which evaluates to "" on triggers that don't carry the input.
+    issue_env = os.environ.get("ISSUE_NUMBER", "").strip()
+    if issue_env:
+        return int(issue_env)
     event_path = os.environ.get("GITHUB_EVENT_PATH", "")
     if event_path and os.path.isfile(event_path):
         with open(event_path) as f:

test_scout.py

@@ -64,13 +64,20 @@ def test_from_event_file(self, tmp_path):
         event = {"issue": {"number": 7}}
         event_file = tmp_path / "event.json"
         event_file.write_text(json.dumps(event))
-        with patch.dict(os.environ, {"ISSUE_NUMBER": "", "GITHUB_EVENT_PATH": str(event_file)}):
-            # Remove ISSUE_NUMBER key entirely so the function falls through to the file
-            env = dict(os.environ)
-            env.pop("ISSUE_NUMBER", None)
-            with patch.dict(os.environ, env, clear=True):
-                os.environ["GITHUB_EVENT_PATH"] = str(event_file)
-                assert scout._get_issue_number() == 7
+        env = {k: v for k, v in os.environ.items() if k != "ISSUE_NUMBER"}
+        env["GITHUB_EVENT_PATH"] = str(event_file)
+        with patch.dict(os.environ, env, clear=True):
+            assert scout._get_issue_number() == 7
+
+    def test_empty_env_falls_through_to_event_file(self, tmp_path):
+        # Workflows commonly pass `${{ github.event.inputs.foo }}`, which is the
+        # empty string on triggers that don't carry that input. Empty must be
+        # treated as unset so auto-detection from the event payload still works.
+        event = {"issue": {"number": 11}}
+        event_file = tmp_path / "event.json"
+        event_file.write_text(json.dumps(event))
+        with patch.dict(os.environ, {"ISSUE_NUMBER": "", "GITHUB_EVENT_PATH": str(event_file)}, clear=True):
+            assert scout._get_issue_number() == 11
 
     def test_raises_when_missing(self):
         env = {k: v for k, v in os.environ.items() if k not in ("ISSUE_NUMBER", "GITHUB_EVENT_PATH")}