feat(orchestration): retry <runId> — authored by headless pi worker (#26, #27)

Collaboration record (conductor loop, docs/plans/CONDUCTOR.md):
- round 1 (worker session worker-1, 2m28s): retry implemented per spec
- conductor live test exposed spec gap: direct invocation lacked
  launcher env exports
- round 2 (same worker session, 59s): spawnEnv made self-sufficient,
  but used PI_* where compose interpolates MOSAIC_*
- conductor hotfix: 3-line rename to MOSAIC_PROVIDER/MOSAIC_MODEL/
  MOSAIC_DATA_ROOT

Final: node scripts/mosaic-task.mjs retry <runId> re-executes a run's
task snapshot as a new run; live retry replied REMEMBERED; all suites
green (24/32/14 + verify).

Known limitation: retrying a run whose task used a RELATIVE mission path
resolves it against the temp dir; lineage tracking deferred.

Closes #25, closes #26, closes #27

scripts/mosaic-task.mjs

@@ -28,6 +28,7 @@
  */
 
 import fs from "node:fs";
+import os from "node:os";
 import path from "node:path";
 import process from "node:process";
 import { randomBytes } from "node:crypto";
@@ -263,6 +264,15 @@ function runTask(taskFile) {
   // CONTAINER path (dataRoot maps to /var/lib/mosaic in the image).
   const spawnEnv = { ...process.env };
   spawnEnv.MOSAIC_ADAPTER = resolved.execution.adapter;
+  // Self-sufficient env: direct invocation (e.g. `retry`) skips the shell
+  // launcher exports, so derive them from the resolved config and release.
+  // (Names here are the compose interpolation consumers, not PI_*.)
+  spawnEnv.MOSAIC_PROVIDER = resolved.execution.provider;
+  spawnEnv.MOSAIC_MODEL = resolved.execution.model;
+  spawnEnv.MOSAIC_DATA_ROOT = resolved.dataRoot;
+  const release = fs.readFileSync(path.join(PROJECT_ROOT, "RELEASE"), "utf8").trim();
+  const piVersion = JSON.parse(fs.readFileSync(path.join(PROJECT_ROOT, "package.json"), "utf8")).dependencies["@earendil-works/pi-coding-agent"];
+  spawnEnv.MOSAIC_IMAGE_TAG = `mosaic-poc-agent:${piVersion}-r${release}`;
   if (task.missionSnapshot) {
     const relative = path.relative(resolved.dataRoot, runDir);
     if (relative.startsWith("..") || path.isAbsolute(relative)) {
@@ -428,6 +438,38 @@ function showRun(runId) {
   process.exit(0);
 }
 
+function retryRun(runId) {
+  if (!/^r-[A-Za-z0-9][A-Za-z0-9._-]{0,63}$/.test(runId)) {
+    fail(4, `invalid run id: ${JSON.stringify(runId)} (expected r-<id>)`);
+  }
+  const resolved = loadConfig();
+  const dir = path.join(runsRoot(resolved), runId);
+  if (!fs.existsSync(dir)) {
+    fail(4, `run not found: ${runId}`);
+  }
+
+  let snapshot;
+  try {
+    snapshot = fs.readFileSync(path.join(dir, "task.json"), "utf8");
+  } catch {
+    fail(4, `run task snapshot unreadable: ${runId}`);
+  }
+
+  // A retry is a brand-new run: replay the recorded task snapshot through
+  // the ordinary run path; existing run records stay untouched.
+  const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "mosaic-retry-"));
+  const tempTaskFile = path.join(tempDir, "task.json");
+  fs.writeFileSync(tempTaskFile, snapshot);
+  process.on("exit", () => {
+    try {
+      fs.rmSync(tempDir, { recursive: true, force: true });
+    } catch {
+      // Best-effort cleanup only.
+    }
+  });
+  runTask(tempTaskFile);
+}
+
 const operation = process.argv[2];
 const target = process.argv[3];
 
@@ -451,6 +493,10 @@ switch (operation) {
   case "list":
     listRuns();
     process.exit(0);
+  case "retry":
+    if (!target) fail(4, "usage: mosaic-task.mjs retry <runId>");
+    retryRun(target);
+    break;
   default:
-    fail(4, `unknown operation: ${JSON.stringify(operation ?? "")} (expected validate | run | show | list)`);
+    fail(4, `unknown operation: ${JSON.stringify(operation ?? "")} (expected validate | run | show | list | retry)`);
 }