feat(mosaic): WI-2 mutator-class guard for directive-freshness (#837)

WI-2: mutator-class guard for the compaction directive-freshness mechanism — command-position parser (prefix x var-indirection unified) + primitive-anchored invariant backstop + all-tools-hook fail-close. Parser-complete on principle: realistic evasion matrix RED-regression-covered, residual exotic evasions proven backstop-caught (B-tests), lens-convergence reached.

closes #829

packages/coord/src/runner.ts

@@ -179,32 +179,41 @@ function buildContinuationPrompt(params: {
     `3. Read \`${mission.scratchpadFile}\` for session history and decisions`,
     `4. Read \`${mission.tasksFile}\` for current task state`,
     '5. `git pull --rebase` to sync latest changes',
-    `6. Launch runtime with \`${runtime} -p\``,
+    `6. Launch runtime with \`mosaic ${runtime} -p\``,
     `7. Continue execution from task **${taskId}**`,
     '8. Follow Two-Phase Completion Protocol',
     `9. You are the SOLE writer of \`${mission.tasksFile}\``,
   ].join('\n');
 }
 
-function resolveLaunchCommand(
+export function resolveLaunchCommand(
   runtime: 'claude' | 'codex',
   prompt: string,
   configuredCommand: string[] | undefined,
 ): string[] {
   if (configuredCommand === undefined || configuredCommand.length === 0) {
-    return [runtime, '-p', prompt];
+    return runtime === 'claude' ? ['mosaic', 'claude', '-p', prompt] : [runtime, '-p', prompt];
   }
 
   const hasPromptPlaceholder = configuredCommand.some((value) => value === '{prompt}');
   const withInterpolation = configuredCommand.map((value) =>
     value === '{prompt}' ? prompt : value,
   );
+  const command = hasPromptPlaceholder ? withInterpolation : [...withInterpolation, prompt];
 
-  if (hasPromptPlaceholder) {
-    return withInterpolation;
+  if (runtime !== 'claude') return command;
+  if (
+    command[0] === 'mosaic' &&
+    (command[1] === 'claude' || (command[1] === 'yolo' && command[2] === 'claude'))
+  ) {
+    return command;
   }
-
-  return [...withInterpolation, prompt];
+  if (command[0] === 'claude') {
+    return ['mosaic', 'claude', ...command.slice(1)];
+  }
+  throw new Error(
+    'Custom Claude task commands must use `mosaic claude` so lease registration cannot be bypassed.',
+  );
 }
 
 async function writeAtomicJson(filePath: string, payload: unknown): Promise<void> {