fix(#792): guard fleet regen roster reads

Dockerfile.ci

@@ -22,10 +22,10 @@
 FROM node:24-alpine
 
 # Native toolchain required to compile node-gyp deps on musl, plus the
-# postgresql-client used by the test step's pg_isready readiness probe. `bash`,
+# postgresql-client used by the test step's pg_isready readiness probe. `bash`
-# `git`, and `jq` are baked here too — framework shell tests and the shipped
+# is baked here too — the sanitization step in ci.yml otherwise does a per-run
-# Codex review wrappers require them without per-run installation in ci.yml.
+# `apk add bash`.
-RUN apk add --no-cache python3 make g++ postgresql-client bash git jq
+RUN apk add --no-cache python3 make g++ postgresql-client bash
 
 # Pin pnpm to the repo's packageManager version via corepack.
 RUN corepack enable && corepack prepare pnpm@10.6.2 --activate

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

@@ -0,0 +1,36 @@
+# ms-792 — Fleet roster error handling and installer heading
+
+## Objective
+
+Make expected missing or malformed fleet roster configuration fail with an actionable message and nonzero exit instead of a raw Node stack trace. Ensure the installer preserves the `@mosaicstack/mosaic` heading.
+
+## Plan
+
+1. Add failing coverage for missing and malformed roster input.
+2. Centralize roster-file read and parse error translation; add the CLI async error boundary.
+3. Sweep fleet command read paths that bypass the roster loader.
+4. Replace the installer heading output with format-safe rendering and test it.
+5. Run focused and repository quality checks; request independent review.
+
+## Progress
+
+- 2026-07-16: Confirmed issue #792 and branch base `9745bc3f`.
+- 2026-07-16: Installed locked workspace dependencies using a worktree-local pnpm store; no `.mosaic/` files were changed intentionally.
+- 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
+
+- `pnpm --filter @mosaicstack/mosaic test` — PASS (61 files, 1,046 tests; executed outside sandbox because CLI smoke tests spawn Node)
+- `pnpm typecheck` — PASS
+- `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
+
+- Dependency installation is required before executing Vitest, TypeScript, lint, and formatting gates.

packages/mosaic/framework/tools/codex/README.md

@@ -70,8 +70,6 @@ Security vulnerability review focusing on:
 ~/.config/mosaic/tools/codex/codex-security-review.sh -n 42
 ```
 
-PR mode resolves the provider's PR diff rather than relying on the caller's checked-out branch. On Gitea, it fetches the base and `refs/pull/<number>/head` refs and diffs those explicit refs. If the refs cannot be fetched or the resulting diff is empty, the command exits nonzero before Codex runs or a review is posted.
-
 ### Review Against Base Branch
 
 ```bash
@@ -255,7 +253,7 @@ Run the script from inside a git repository.
 
 ### "No changes found to review"
 
-The specified non-PR mode (`--uncommitted`, `--base`, etc.) found no changes to review. PR mode instead fails closed with an actionable error when it cannot construct a non-empty provider diff; verify the PR number, remote, provider login, and ref access before retrying.
+The specified mode (--uncommitted, --base, etc.) found no changes to review.
 
 ### "Codex produced no output"
 

packages/mosaic/framework/tools/codex/common.sh

@@ -44,47 +44,38 @@ build_diff_context() {
             diff_text=$(git show "$value" 2>/dev/null)
             ;;
         pr)
-            # Provider detection writes its result to stdout; suppress it so it cannot
+            # For PRs, we need to fetch the PR diff
-            # be mistaken for diff content when this function is used in a substitution.
+            detect_platform
-            detect_platform >/dev/null
             if [[ "$PLATFORM" == "github" ]]; then
-                diff_text=$(gh pr diff "$value" 2>/dev/null) || {
+                diff_text=$(gh pr diff "$value" 2>/dev/null)
-                    echo "Error: Failed to fetch the diff for PR #${value}." >&2
-                    return 1
-                }
             elif [[ "$PLATFORM" == "gitea" ]]; then
-                local pr_base base_ref pr_head_ref
+                # tea doesn't have a direct pr diff command, use git
-                pr_base=$(tea pr list --fields index,base --output simple 2>/dev/null | awk -v pr="$value" '$1 == pr { print $2; exit }')
+                local pr_base
-                if [[ -z "$pr_base" ]]; then
+                pr_base=$(tea pr list --fields index,base --output simple 2>/dev/null | grep "^${value}" | awk '{print $2}')
-                    echo "Error: Could not resolve the base branch for Gitea PR #${value}." >&2
+                if [[ -n "$pr_base" ]]; then
-                    return 1
+                    diff_text=$(git diff "${pr_base}...HEAD" 2>/dev/null)
+                else
+                    # Fallback: fetch PR info via API
+                    local repo_info
+                    repo_info=$(get_repo_info)
+                    local remote_url
+                    remote_url=$(git remote get-url origin 2>/dev/null)
+                    local host
+                    host=$(echo "$remote_url" | sed -E 's|.*://([^/]+).*|\1|; s|.*@([^:]+).*|\1|')
+                    diff_text=$(curl -s "https://${host}/api/v1/repos/${repo_info}/pulls/${value}" \
+                        -H "Authorization: token $(tea login list --output simple 2>/dev/null | head -1 | awk '{print $2}')" \
+                        2>/dev/null | jq -r '.diff_url // empty')
+                    if [[ -n "$diff_text" && "$diff_text" != "null" ]]; then
+                        diff_text=$(curl -s "$diff_text" 2>/dev/null)
+                    else
+                        diff_text=$(git diff "main...HEAD" 2>/dev/null)
+                    fi
                 fi
-
-                base_ref="refs/remotes/origin/${pr_base}"
-                pr_head_ref="refs/remotes/origin/pr/${value}/head"
-                if ! git fetch --quiet origin \
-                    "+refs/heads/${pr_base}:${base_ref}" \
-                    "+refs/pull/${value}/head:${pr_head_ref}"; then
-                    echo "Error: Failed to fetch the base and head refs for Gitea PR #${value}." >&2
-                    return 1
-                fi
-                diff_text=$(git diff "${base_ref}...${pr_head_ref}") || {
-                    echo "Error: Failed to diff the fetched refs for Gitea PR #${value}." >&2
-                    return 1
-                }
-            else
-                echo "Error: Unsupported git platform while resolving PR #${value}." >&2
-                return 1
             fi
             ;;
     esac
 
-    if [[ "$mode" == "pr" && -z "${diff_text//[[:space:]]/}" ]]; then
+    echo "$diff_text"
-        echo "Error: Unable to construct a non-empty diff for PR #${value}; verify the PR refs and provider access." >&2
-        return 1
-    fi
-
-    printf '%s\n' "$diff_text"
 }
 
 # Format JSON findings as markdown for PR comments

packages/mosaic/framework/tools/codex/test-pr-diff-context.sh

@@ -1,158 +0,0 @@
-#!/bin/bash
-# Hermetic regression coverage for Gitea PR diff construction and fail-closed reviews.
-set -euo pipefail
-
-SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-TMP_DIR=$(mktemp -d)
-trap 'rm -rf "$TMP_DIR"' EXIT
-
-fail() {
-    echo "not ok - $*" >&2
-    exit 1
-}
-
-assert_contains() {
-    local haystack="$1" needle="$2"
-    if [[ "$haystack" != *"$needle"* ]]; then
-        printf 'actual output:\n%s\n' "$haystack" >&2
-        fail "expected output to contain: $needle"
-    fi
-}
-
-# Prevent CI-provided repository context from leaking into the fixture repositories.
-unset GIT_DIR GIT_WORK_TREE GIT_INDEX_FILE GIT_OBJECT_DIRECTORY \
-    GIT_ALTERNATE_OBJECT_DIRECTORIES GIT_COMMON_DIR
-export GIT_AUTHOR_NAME="Codex Fixture"
-export GIT_AUTHOR_EMAIL="codex-fixture@example.test"
-export GIT_COMMITTER_NAME="$GIT_AUTHOR_NAME"
-export GIT_COMMITTER_EMAIL="$GIT_AUTHOR_EMAIL"
-export GITEA_LOGIN="fixture"
-export GITEA_TOKEN="fixture-token"
-export GITEA_URL="file://$TMP_DIR"
-
-create_pr_fixture() {
-    local fixture_root="$1" head_mode="$2"
-    local origin="$fixture_root/origin.git"
-    local seed="$fixture_root/seed"
-    local work="$fixture_root/work"
-    local base_sha head_sha
-
-    mkdir -p "$fixture_root"
-    git init --quiet --bare "$origin"
-    git init --quiet --initial-branch=release/next "$seed"
-    printf 'base\n' > "$seed/pr-change.ts"
-    git -C "$seed" add pr-change.ts
-    git -C "$seed" commit --quiet -m "fixture base"
-    base_sha=$(git -C "$seed" rev-parse HEAD)
-    git -C "$seed" remote add origin "$origin"
-    git -C "$seed" push --quiet origin release/next
-    git --git-dir="$origin" symbolic-ref HEAD refs/heads/release/next
-
-    if [[ "$head_mode" == "changed" ]]; then
-        git -C "$seed" switch --quiet -c feature/pr-795
-        printf 'actual-pr-change\n' > "$seed/pr-change.ts"
-        git -C "$seed" commit --quiet -am "fixture PR head"
-        head_sha=$(git -C "$seed" rev-parse HEAD)
-        git -C "$seed" push --quiet origin HEAD:refs/pull/795/head
-    else
-        head_sha="$base_sha"
-        git --git-dir="$origin" update-ref refs/pull/795/head "$head_sha"
-    fi
-
-    # Gitea's provider-owned PR head ref now exists in the local bare origin.
-    git clone --quiet "$origin" "$work"
-    printf '%s\n' "$work"
-}
-
-FAKE_BIN="$TMP_DIR/bin"
-mkdir -p "$FAKE_BIN"
-cat > "$FAKE_BIN/tea" <<'STUB'
-#!/bin/bash
-if [[ "$*" == "pr list --fields index,base --output simple" ]]; then
-    printf '795 release/next\n'
-    exit 0
-fi
-exit 1
-STUB
-cat > "$FAKE_BIN/codex" <<'STUB'
-#!/bin/bash
-printf 'CODEX %s\n' "$*" >> "$CODEX_LOG"
-exit 99
-STUB
-chmod +x "$FAKE_BIN/tea" "$FAKE_BIN/codex"
-export PATH="$FAKE_BIN:$PATH"
-
-# The valid fixture is a fresh clone on the non-main base. The PR head exists only
-# at refs/pull/795/head, so local HEAD cannot accidentally satisfy the assertion.
-if [[ "${1:-all}" != "fail-closed" ]]; then
-    VALID_WORK=$(create_pr_fixture "$TMP_DIR/valid" changed)
-    (
-        cd "$VALID_WORK"
-        # shellcheck source=common.sh
-        source "$SCRIPT_DIR/common.sh"
-        diff_context=$(build_diff_context pr 795)
-        assert_contains "$diff_context" "actual-pr-change"
-
-        base_sha=$(git rev-parse refs/remotes/origin/release/next)
-        head_sha=$(git rev-parse refs/remotes/origin/pr/795/head)
-        local_sha=$(git rev-parse HEAD)
-        [[ "$local_sha" == "$base_sha" ]] || fail "fixture clone is not on the PR base"
-        [[ "$head_sha" != "$base_sha" ]] || fail "fixture PR head does not differ from its base"
-        git show-ref --verify --quiet refs/remotes/origin/pr/795/head || \
-            fail "fetched PR head ref is missing"
-        [[ "$(git diff --name-only "${base_sha}...${head_sha}")" == "pr-change.ts" ]] || \
-            fail "explicit PR refs do not contain the fixture change"
-        if git show-ref --verify --quiet refs/heads/main || \
-            git show-ref --verify --quiet refs/remotes/origin/main; then
-            fail "fixture unexpectedly contains a main ref"
-        fi
-    )
-    echo "ok - Gitea PR mode fetches and diffs explicit non-main base and PR head refs"
-fi
-
-# Build an empty PR entirely inside another local repository. Both review wrappers
-# must emit the PR-numbered error before Codex or the stubbed post path can execute.
-if [[ "${1:-all}" != "pr-head" ]]; then
-    EMPTY_WORK=$(create_pr_fixture "$TMP_DIR/empty" empty)
-    SANDBOX="$TMP_DIR/sandbox"
-    mkdir -p "$SANDBOX/tools/codex/schemas" "$SANDBOX/tools/git"
-    cp "$SCRIPT_DIR/common.sh" \
-        "$SCRIPT_DIR/codex-code-review.sh" \
-        "$SCRIPT_DIR/codex-security-review.sh" \
-        "$SANDBOX/tools/codex/"
-    cp "$SCRIPT_DIR/schemas/code-review-schema.json" \
-        "$SCRIPT_DIR/schemas/security-review-schema.json" \
-        "$SANDBOX/tools/codex/schemas/"
-    cp "$SCRIPT_DIR/../git/detect-platform.sh" "$SANDBOX/tools/git/"
-
-    cat > "$SANDBOX/tools/git/pr-review.sh" <<'STUB'
-#!/bin/bash
-printf 'POST %s\n' "$*" >> "$POST_LOG"
-STUB
-    chmod +x "$SANDBOX/tools/git/pr-review.sh"
-
-    POST_LOG="$TMP_DIR/post.log"
-    CODEX_LOG="$TMP_DIR/codex.log"
-    export POST_LOG CODEX_LOG
-
-    for review_kind in code security; do
-        : > "$POST_LOG"
-        : > "$CODEX_LOG"
-        review_script="$SANDBOX/tools/codex/codex-${review_kind}-review.sh"
-        set +e
-        (
-            cd "$EMPTY_WORK"
-            "$review_script" -n 795
-        ) >"$TMP_DIR/${review_kind}.stdout" 2>"$TMP_DIR/${review_kind}.stderr"
-        review_status=$?
-        set -e
-
-        stderr_text=$(cat "$TMP_DIR/${review_kind}.stderr")
-        [[ "$review_status" -ne 0 ]] || fail "${review_kind} review returned success for an empty PR diff"
-        [[ ! -s "$CODEX_LOG" ]] || fail "Codex ran for an empty ${review_kind} PR diff"
-        [[ ! -s "$POST_LOG" ]] || fail "${review_kind} review auto-post ran for an empty PR diff"
-        assert_contains "$stderr_text" "Error:"
-        assert_contains "$stderr_text" "PR #795"
-        echo "ok - empty ${review_kind} PR diff fails closed before Codex and auto-post"
-    done
-fi

packages/mosaic/package.json

@@ -24,8 +24,7 @@
     "build": "tsc",
     "lint": "eslint src",
     "typecheck": "tsc --noEmit",
-    "test": "vitest run --passWithNoTests && pnpm run test:framework-shell",
+    "test": "vitest run --passWithNoTests"
-    "test:framework-shell": "bash framework/tools/codex/test-pr-diff-context.sh"
   },
   "dependencies": {
     "@mosaicstack/brain": "workspace:*",

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`);

packages/mosaic/src/commands/fleet.spec.ts

@@ -60,6 +60,7 @@ import {
   type SleepFn,
 } from './fleet.js';
 import { registerAgentCommand } from './agent.js';
+import { parseFleetRosterDocument, readFleetRosterText } from '../fleet/fleet-roster-v1.js';
 
 function buildProgram(): Command {
   const program = new Command();
@@ -166,6 +167,55 @@ describe('registerFleetCommand', () => {
   });
 });
 
+describe('fleet roster configuration failures', () => {
+  it('reports a missing roster with an actionable initialization hint', async () => {
+    const home = await tempDir();
+    try {
+      const program = buildProgram();
+
+      await expect(
+        program.parseAsync(['node', 'mosaic', 'fleet', '--mosaic-home', home, 'ps']),
+      ).rejects.toThrow(
+        `No fleet roster found at ${join(home, 'fleet', 'roster.json')}. Run \`mosaic fleet init\``,
+      );
+    } finally {
+      await rm(home, { recursive: true, force: true });
+    }
+  });
+
+  it('reports a malformed roster with the path and repair hint', async () => {
+    const home = await tempDir();
+    const rosterPath = join(home, 'fleet', 'roster.json');
+    try {
+      await mkdir(dirname(rosterPath), { recursive: true });
+      await writeFile(rosterPath, '{not valid json');
+
+      await expect(loadFleetRoster(rosterPath)).rejects.toThrow(
+        `Fleet roster at ${rosterPath} is invalid. Fix the file or run \`mosaic fleet init --force\``,
+      );
+    } finally {
+      await rm(home, { recursive: true, force: true });
+    }
+  });
+
+  it('reports an unreadable roster without exposing the filesystem error', async () => {
+    const home = await tempDir();
+    try {
+      await expect(readFleetRosterText(home)).rejects.toThrow(
+        `Could not read fleet roster at ${home}. Check the file exists and is readable.`,
+      );
+    } finally {
+      await rm(home, { recursive: true, force: true });
+    }
+  });
+
+  it('reports a malformed roster while selecting the v1/v2 command path', () => {
+    expect(() => parseFleetRosterDocument('version: [', '/srv/mosaic/fleet/roster.yaml')).toThrow(
+      'Fleet roster at /srv/mosaic/fleet/roster.yaml is invalid. Fix the file or run `mosaic fleet init --force`.',
+    );
+  });
+});
+
 describe('fleet roster parsing', () => {
   let cleanup: string | undefined;
 

packages/mosaic/src/commands/fleet.ts

@@ -19,8 +19,11 @@ import * as readline from 'node:readline';
 import type { Command } from 'commander';
 import YAML from 'yaml';
 import {
+  FleetRosterConfigurationError,
   getRosterAgent,
   loadFleetRoster,
+  parseFleetRosterDocument,
+  readFleetRosterText,
   resolveInstalledFleetRosterPath,
   type FleetAgent,
   type FleetRoster,
@@ -1913,7 +1916,7 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
         const commandOpts = cmd.opts<{ mosaicHome: string; roster?: string }>();
         const activePaths = resolveFleetPaths(commandOpts.mosaicHome);
         const rosterPath = await resolveRosterPath(commandOpts.mosaicHome, commandOpts.roster);
-        const roster = await loadFleetRoster(rosterPath);
+        const roster = await loadRosterAtPath(cmd, rosterPath);
 
         const newAgent: FleetAgent = {
           name,
@@ -1973,7 +1976,7 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
       const commandOpts = cmd.opts<{ mosaicHome: string; roster?: string }>();
       const activePaths = resolveFleetPaths(commandOpts.mosaicHome);
       const rosterPath = await resolveRosterPath(commandOpts.mosaicHome, commandOpts.roster);
-      const roster = await loadFleetRoster(rosterPath);
+      const roster = await loadRosterAtPath(cmd, rosterPath);
 
       // Guard: throws if removing leaves 0 orchestrators or agent not in roster
       const updatedRoster = removeAgentFromRoster(roster, name);
@@ -2402,14 +2405,19 @@ async function installFleet(cmd: Command, frameworkRoot: string): Promise<void>
 
 async function loadRosterForCommand(cmd: Command): Promise<FleetRoster> {
   const opts = cmd.opts<{ mosaicHome: string; roster?: string }>();
-  return loadFleetRoster(await resolveRosterPath(opts.mosaicHome, opts.roster));
+  return loadRosterAtPath(cmd, await resolveRosterPath(opts.mosaicHome, opts.roster));
 }
 
 /** Routes only a v2 roster to the M3 desired-state control plane; v1 aliases stay compatible. */
 async function usesRosterV2ControlPlane(cmd: Command): Promise<boolean> {
   const opts = cmd.opts<{ mosaicHome: string; roster?: string }>();
   const path = await resolveRosterPath(opts.mosaicHome, opts.roster);
-  const parsed: unknown = YAML.parse(await readFile(path, 'utf8'));
+  let parsed: unknown;
+  try {
+    parsed = parseFleetRosterDocument(await readFleetRosterText(path), path);
+  } catch (error) {
+    reportFleetRosterConfigurationError(cmd, error);
+  }
   return (
     typeof parsed === 'object' &&
     parsed !== null &&
@@ -2425,7 +2433,22 @@ async function loadRosterFromAgentCommand(
 ): Promise<FleetRoster> {
   const opts = command.optsWithGlobals<{ mosaicHome?: string; roster?: string }>();
   const mosaicHome = opts.mosaicHome ?? mosaicHomeOverride ?? defaultMosaicHome();
-  return loadFleetRoster(await resolveRosterPath(mosaicHome, opts.roster));
+  return loadRosterAtPath(command, await resolveRosterPath(mosaicHome, opts.roster));
+}
+
+async function loadRosterAtPath(command: Command, path: string): Promise<FleetRoster> {
+  try {
+    return await loadFleetRoster(path);
+  } catch (error) {
+    reportFleetRosterConfigurationError(command, error);
+  }
+}
+
+function reportFleetRosterConfigurationError(command: Command, error: unknown): never {
+  if (error instanceof FleetRosterConfigurationError) {
+    command.error(error.message, { code: 'fleet.roster', exitCode: 1 });
+  }
+  throw error;
 }
 
 function resolveMosaicHomeFromCommand(command: Command, override?: string): string {

packages/mosaic/src/commands/install-heading.spec.ts

@@ -0,0 +1,17 @@
+import { readFile } from 'node:fs/promises';
+import { fileURLToPath } from 'node:url';
+import { describe, expect, it } from 'vitest';
+
+const INSTALLER_PATH = fileURLToPath(new URL('../../../../tools/install.sh', import.meta.url));
+
+describe('installer CLI package heading', () => {
+  it('renders the scoped package name intact', async () => {
+    const installer = await readFile(INSTALLER_PATH, 'utf8');
+    const step = installer.match(/^step\(\)\s*\{.*\}$/m)?.[0];
+
+    expect(step).toBeDefined();
+
+    expect(step).toContain('printf \'\\n%s%s%s\\n\' "$BOLD" "$*" "$RESET"');
+    expect(installer).toContain('step "@mosaicstack/mosaic (npm package)"');
+  });
+});

packages/mosaic/src/fleet/fleet-roster-v1.ts

@@ -104,6 +104,10 @@ export interface FleetRoster {
 
 export type FleetRosterInputFormat = 'yaml' | 'json';
 
+export class FleetRosterConfigurationError extends Error {
+  override name = 'FleetRosterConfigurationError';
+}
+
 export function resolveInstalledFleetRosterPath(mosaicHome: string): string {
   const yamlPath = join(mosaicHome, 'fleet', 'roster.yaml');
   try {
@@ -138,8 +142,52 @@ export function parseFleetRosterV1(
 }
 
 export async function loadFleetRoster(path: string): Promise<FleetRoster> {
-  const source = await readFile(path, 'utf8');
+  const source = await readFleetRosterText(path);
-  return parseFleetRosterV1(source, path.endsWith('.json') ? 'json' : 'yaml');
+  try {
+    return parseFleetRosterV1(source, path.endsWith('.json') ? 'json' : 'yaml');
+  } catch (error) {
+    if (isRosterParserError(error)) throw invalidFleetRosterError(path);
+    throw error;
+  }
+}
+
+/** Read an operator-owned roster with errors that say how to recover. */
+export async function readFleetRosterText(path: string): Promise<string> {
+  try {
+    return await readFile(path, 'utf8');
+  } catch (error) {
+    if (isNodeErrorCode(error, 'ENOENT')) {
+      throw new FleetRosterConfigurationError(
+        `No fleet roster found at ${path}. Run \`mosaic fleet init\` to create one.`,
+      );
+    }
+    throw new FleetRosterConfigurationError(
+      `Could not read fleet roster at ${path}. Check the file exists and is readable.`,
+    );
+  }
+}
+
+/** Parse a roster document needed only to select the v1/v2 command path. */
+export function parseFleetRosterDocument(source: string, path: string): unknown {
+  try {
+    return YAML.parse(source);
+  } catch (error) {
+    if (isRosterParserError(error)) throw invalidFleetRosterError(path);
+    throw error;
+  }
+}
+
+function invalidFleetRosterError(path: string): FleetRosterConfigurationError {
+  return new FleetRosterConfigurationError(
+    `Fleet roster at ${path} is invalid. Fix the file or run \`mosaic fleet init --force\`.`,
+  );
+}
+
+function isRosterParserError(error: unknown): boolean {
+  return (
+    error instanceof SyntaxError ||
+    (error instanceof Error && (error.name === 'YAMLParseError' || error.name === 'YAMLWarning'))
+  );
 }
 
 export function getRosterAgent(roster: FleetRoster, name: string): FleetAgent {

tools/install.sh

@@ -212,7 +212,7 @@ ok()    { echo "${G}✔${RESET}  $*"; }
 warn()  { echo "${Y}⚠${RESET}  $*"; }
 fail()  { echo "${R}✖${RESET}  $*" >&2; }
 dim()   { echo "${DIM}$*${RESET}"; }
-step()  { echo ""; echo "${BOLD}$*${RESET}"; }
+step()  { printf '\n%s%s%s\n' "$BOLD" "$*" "$RESET"; }
 
 # ─── helpers ──────────────────────────────────────────────────────────────────