fix(ci): require a line range for context evidence

The tri-review's adversarial lane executed `context({name: 'AGENTS.md'})`
and had the result accepted: the gate checked only that the resolved
filePath was in the changed set, so a bare File node passed for a review
of that file's contents. The trusted prescan already defines an indexable
symbol as one with startLine and endLine, so require the same here.

Pre-existing rather than introduced by this branch, but it is the same
"what counts as proof" surface the rest of this PR tightens.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/gitnexus-review-agent.yml

@@ -1748,11 +1748,16 @@ jobs:
               throw new Error('context tool result is not strict JSON');
             }
             validateBoundedJson(decoded, { nodes: 0 });
+            // A line range is what the trusted prescan calls an indexable
+            // symbol, so a bare File node — `context({name: 'AGENTS.md'})` —
+            // must not pass for a review of that file's contents.
             if (
               !isRecord(decoded) ||
               Object.hasOwn(decoded, 'error') ||
               decoded.status !== 'found' ||
-              !isRecord(decoded.symbol)
+              !isRecord(decoded.symbol) ||
+              !Number.isFinite(decoded.symbol.startLine) ||
+              !Number.isFinite(decoded.symbol.endLine)
             ) {
               rejected.unresolved += 1;
               return false;

gitnexus/test/unit/review-agent-workflow.test.ts

@@ -1776,6 +1776,27 @@ describe('gitnexus review-agent workflow security contract', () => {
     expect(structural.artifact.failure_code).toBe('invalid_execution_transcript');
   });
 
+  it('refuses a bare File node as evidence, matching the prescan definition of indexable', () => {
+    const fileNode = runArtifactScenario({
+      rawTranscript: JSON.stringify(
+        reviewTranscript({
+          toolInput: { name: 'status.ts' },
+          toolResultContent: JSON.stringify({
+            status: 'found',
+            symbol: {
+              uid: `File:${CHANGED_PATH}`,
+              name: 'status.ts',
+              kind: 'File',
+              filePath: CHANGED_PATH,
+            },
+          }),
+        }),
+      ),
+    });
+    expect(fileNode.artifact.failure_code).toBe('missing_graph_evidence');
+    expect(fileNode.stderr).toContain('results that resolved nothing: 1');
+  });
+
   it('scopes a deletion-only PR to the merge-base set instead of an empty head set', () => {
     const deletedPath = 'gitnexus/src/cli/deleted-command.ts';
     const headScopedCall = runArtifactScenario({