fix(sast): align Capella export with the submit-time code-path contract

The export gate required every code_paths entry to be file:line, but submit only
requires the primary sink to be file:line and accepts bare trace steps. A single
malformed trace step therefore dropped an otherwise-valid finding at export.

- add isValidPrimaryCodePath as the one shared primary-sink contract
- validate only the primary at export; buildResult already drops unusable steps
- route the submit-time validator through the same helper so the two cannot drift

apps/worker/src/ai/sast/capella/collectors.ts

@@ -55,7 +55,7 @@ import {
   type TriageChecklist,
   type TriageRuleKey,
 } from './finding-types.js';
-import { isNormalizedRepositoryPath, parseCodePath } from './paths.js';
+import { isValidPrimaryCodePath, parseCodePath } from './paths.js';
 
 // === Result Helpers ===
 
@@ -265,8 +265,7 @@ export function validateCodePaths(
       error: `code_paths[0] must be a sink location "<path>:<line>", not a URL (got ${JSON.stringify(first)}).`,
     };
   }
-  const parsed = parseCodePath(first);
-  if (!parsed || !isNormalizedRepositoryPath(parsed.file)) {
+  if (!isValidPrimaryCodePath(first)) {
     return {
       ok: false,
       error:
@@ -275,6 +274,10 @@ export function validateCodePaths(
         'contain traversal, be a bare file, a symbol or an offset.',
     };
   }
+  const parsed = parseCodePath(first);
+  if (!parsed) {
+    return { ok: false, error: 'code_paths[0] must be a "<path>:<line>" locator.' };
+  }
   return { ok: true, codePaths, file: parsed.file, line: parsed.line };
 }
 

apps/worker/src/ai/sast/capella/paths.ts

@@ -21,6 +21,17 @@ export function parseCodePath(entry: string): ParsedCodePath | undefined {
   return { file, line };
 }
 
+/**
+ * The primary (sink) code-path contract, shared by the submit-time collector and the
+ * export gate so the two ends enforce the same rule and cannot drift. `code_paths[0]`
+ * becomes the finding's SARIF location, so it must be a normalized repository-relative
+ * `file:line`. Trace steps are held to no such requirement on either side.
+ */
+export function isValidPrimaryCodePath(entry: string): boolean {
+  const parsed = parseCodePath(entry);
+  return parsed !== undefined && isNormalizedRepositoryPath(parsed.file);
+}
+
 /**
  * The normalized repository-relative POSIX path contract shared by SARIF
  * locations and code-path scoping. Rejects absolute, drive-letter, encoded,

apps/worker/src/ai/sast/capella/sarif-exporter.ts

@@ -22,7 +22,7 @@ import type { AgenticSastOmission, AgenticSastReduction, SarifRef } from '../typ
 import { atomicPublishBytes, sha256Bytes, stableJson } from './artifacts.js';
 import { SastContractError } from './errors.js';
 import type { CapellaFinding, CapellaSeverity } from './finding-types.js';
-import { isExcludedCodePath, isNormalizedRepositoryPath, parseCodePath } from './paths.js';
+import { isExcludedCodePath, isNormalizedRepositoryPath, isValidPrimaryCodePath, parseCodePath } from './paths.js';
 import { renderCapellaReport } from './report.js';
 import type { AtomicPublishOptions } from './types.js';
 import { isCapellaFinding } from './validation.js';
@@ -102,14 +102,15 @@ function classifyExportCandidate(
   if (!isCapellaFinding(value)) {
     return { omission: buildOmission(value, 'invalid_finding_record') };
   }
-  if (value.code_paths.length === 0) {
+  const primary = value.code_paths[0];
+  if (value.code_paths.length === 0 || primary === undefined) {
     return { omission: buildOmission(value, 'missing_code_path') };
   }
-  const codePathsAreValid = value.code_paths.every((entry) => {
-    const parsed = parseCodePath(entry);
-    return parsed !== undefined && isNormalizedRepositoryPath(parsed.file);
-  });
-  if (!codePathsAreValid) {
+  // Only the primary (sink) must be a `file:line` locator: it becomes the SARIF location.
+  // Trace steps are held to no such rule at submit time, and `buildResult` already drops any
+  // that are not `file:line`, so gating on them here would discard a whole finding for a
+  // malformed step the two ends never agreed to require.
+  if (!isValidPrimaryCodePath(primary)) {
     return { omission: buildOmission(value, 'invalid_code_path') };
   }
   return { finding: value };