fix(#792): guard fleet regen roster reads

docs/scratchpads/ms-792-fleet-enoent-installer.md

@@ -19,6 +19,7 @@ Make expected missing or malformed fleet roster configuration fail with an actio
 - 2026-07-16: Added a shared roster read/parse guard and routed v1 fleet commands plus v1/v2 selection through Commander’s actionable nonzero error path. V2 command modules already return structured nonzero JSON errors for their guarded reads.
 - 2026-07-16: Replaced installer heading `echo` with format-safe `printf`; added a regression check for the scoped package heading.
 - 2026-07-16: Rebuilt CLI and manually verified `fleet ps` with no roster prints the initialization hint, exits 1, and has no stack trace.
+- 2026-07-17: Rebased #818 onto `origin/main` at `9ddc6fbd` (#791 PR3). The added `fleet regen` command had a canonical roster read in its sibling module; it now uses the same missing-roster guard and Commander exit path. Internal NORTH_STAR, preset, and post-write invariant reads remain intentionally unguarded.
 
 ## Verification
 
@@ -27,6 +28,7 @@ Make expected missing or malformed fleet roster configuration fail with an actio
 - `pnpm lint` — PASS
 - `pnpm format:check` — PASS
 - `pnpm --filter @mosaicstack/mosaic exec vitest run src/commands/fleet.spec.ts src/commands/install-heading.spec.ts` — PASS (209 tests)
+- `pnpm --filter @mosaicstack/mosaic exec vitest run src/commands/fleet-regen-command.spec.ts` — PASS (27 tests, including missing canonical roster)
 - Instrumented Vitest coverage is unavailable because `@vitest/coverage-v8` is not declared in this repository. Each branch added in the roster guard has direct unit coverage.
 
 ## Risks / blockers

packages/mosaic/src/commands/fleet-regen-command.spec.ts

@@ -150,6 +150,17 @@ describe('projectRosterV2AgentGeneratedEnv', (): void => {
 });
 
 describe('mosaic fleet regen', (): void => {
+  it('reports a missing canonical roster with the shared initialization hint', async (): Promise<void> => {
+    const home = await mkdtemp(join(tmpdir(), 'mosaic-fleet-regen-missing-roster-'));
+    cleanup = home;
+
+    await expect(
+      program(home, recordingRunner([])).parseAsync(['node', 'mosaic', 'fleet', 'regen', '--json']),
+    ).rejects.toThrow(
+      `No fleet roster found at ${join(home, 'fleet', 'roster.yaml')}. Run \`mosaic fleet init\``,
+    );
+  });
+
   it('is dry-run by default: reports the plan and writes nothing', async (): Promise<void> => {
     const home = await fleetHome();
     const calls: string[][] = [];

packages/mosaic/src/commands/fleet-regen-command.ts

@@ -1,4 +1,4 @@
-import { readFile, stat } from 'node:fs/promises';
+import { stat } from 'node:fs/promises';
 import { homedir } from 'node:os';
 import { join, relative, resolve } from 'node:path';
 import type { Command } from 'commander';
@@ -18,6 +18,7 @@ import {
   validateRosterV2Semantics,
   type FleetRosterV2,
 } from '../fleet/roster-v2.js';
+import { FleetRosterConfigurationError, readFleetRosterText } from '../fleet/fleet-roster-v1.js';
 
 /**
  * `mosaic fleet regen` — recovery-framed regeneration of the roster-derived
@@ -303,7 +304,7 @@ function defaultReadRoster(
   mosaicHome: string,
 ): (rosterPath: string) => Promise<FleetRosterV2> {
   return async (rosterPath: string): Promise<FleetRosterV2> => {
-    const roster = parseRosterV2(await readFile(rosterPath, 'utf8'), 'yaml');
+    const roster = parseRosterV2(await readFleetRosterText(rosterPath), 'yaml');
     // Enforce the SAME semantic gate as reconcile/plan/verify (persona resolution
     // + protected-class tool-policy match) so regen cannot project a roster the
     // rest of the fleet surface would reject.
@@ -433,6 +434,10 @@ export function registerFleetRegenCommand(fleetCommand: Command, deps: FleetRege
         // the operator must finish/verify (and clear the lock) before restarting.
         if (result.incomplete || result.cleanup) process.exitCode = 1;
       } catch (error: unknown) {
+        if (error instanceof FleetRosterConfigurationError) {
+          fleetCommand.error(error.message, { code: 'fleet.roster', exitCode: 1 });
+          return;
+        }
         process.exitCode = 1;
         const message = error instanceof Error ? error.message : String(error);
         process.stderr.write(`mosaic fleet regen failed: ${message}\n`);