fix(retry): lineage tracking + relative mission path resolution (#28)

- retryRun rewrites a snapshot's relative mission path to the run's own
  recorded mission.json (absolute) before execution — retries stay
  faithful to what originally ran
- runTask accepts options.retriedFrom; retry records lineage in
  result.json (additive optional field, no schema break)
- task suite +4 cases: retry succeeds, lineage recorded, mission section
  present after retry (36 total), missing-run retry exits 4

Closes #28

scripts/test-task.sh

@@ -142,6 +142,21 @@ EOF
         && grep -q 'Seam directive A.' "$SANDBOX/data/system-prompt.md" \
         && check "mission section injected into generated prompt" 0 \
         || check "mission section injected into generated prompt" 1
+
+    # retry lineage + relative mission path resolution
+    expect_exit "retry of mission run succeeds" 0 -- \
+        env MOSAIC_CONFIG="$SANDBOX/mock-adapters.json" MOSAIC_MOCK_RESPONSE=MOCKED \
+        node scripts/mosaic-task.mjs retry "$(ls -dt "$SANDBOX/data/runs"/r-* | head -1 | xargs basename)"
+    RT="$(ls -dt "$SANDBOX/data/runs"/r-* | head -1 | xargs basename)"
+    ORIG="$(ls -dt "$SANDBOX/data/runs"/r-* | sed -n 2p | xargs basename)"
+    node -e 'const r=JSON.parse(require("fs").readFileSync(process.argv[1],"utf8"));process.exit(r.retriedFrom===process.argv[2]?0:1)' \
+        "$SANDBOX/data/runs/$RT/result.json" "$ORIG" \
+        && check "retriedFrom lineage recorded" 0 || check "retriedFrom lineage recorded" 1
+    grep -q 'MISSION (runtime)' "$SANDBOX/data/system-prompt.md" \
+        && check "mission section present after retry (relative path resolved)" 0 \
+        || check "mission section present after retry (relative path resolved)" 1
+    expect_exit "retry of missing run exits 4" 4 -- \
+        env MOSAIC_CONFIG="$SANDBOX/mock-adapters.json" node scripts/mosaic-task.mjs retry r-missing
 else
     echo "skip adapter seam cases (docker daemon unavailable)"
 fi