feat(framework): P4 (1/2) — install.sh upgrade-safe Constitution migration

Make CONSTITUTION/AGENTS/STANDARDS framework-owned (overwritten on upgrade) while
never losing user data:
- FRAMEWORK_OWNED vs USER_SEEDED lists (append-friendly per Lead's ask)
- reconcile_framework_files: overwrite framework-owned from defaults/, backing up a
  divergent copy ONCE to <file>.pre-constitution.bak (advisory); seed-if-absent for
  USER_SEEDED (TOOLS.md)
- anchor rsync preserve excludes to top-level (/<file>) so defaults/<file> still syncs
- never delete *.pre-constitution.bak across upgrades (rsync + cp-fallback)
- snapshot -> sync -> restore-on-failure (ERR/INT/TERM trap) for crash safety
- FRAMEWORK_VERSION 2 -> 3 + v2->v3 migration advisory
- MOSAIC_SYNC_ONLY hook for testability (file phase only, no env side effects)

Fixture suite (test-install-migration.sh) green 7/7: fresh, legacy-edited AGENTS
(overwrite + backup + SOUL/creds survive + idempotent .bak), tuned STANDARDS,
no-TTY, failure-path data integrity. Two real bugs caught + fixed by the fixtures
(unanchored exclude blocking the overwrite; backup deletion on re-upgrade).

file-adapter.ts TS parity + the vitest fixture matrix land in P4 (2/2).

Refs #542

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/mosaic/framework/install.sh

@@ -21,11 +21,19 @@ INSTALL_MODE="${MOSAIC_INSTALL_MODE:-prompt}"
 
 # Files/dirs preserved across upgrades (never overwritten).
 # User-created content in these paths survives rsync --delete.
-PRESERVE_PATHS=("AGENTS.md" "SOUL.md" "USER.md" "TOOLS.md" "STANDARDS.md" "memory" "sources" "credentials")
+PRESERVE_PATHS=("CONSTITUTION.md" "AGENTS.md" "SOUL.md" "USER.md" "TOOLS.md" "STANDARDS.md" "memory" "sources" "credentials")
+
+# Framework-owned contract files: re-copied from defaults/ on every upgrade (the
+# user must not edit them; a divergent copy is backed up once before overwrite).
+# USER_SEEDED files are written once on first install, then owned by the user.
+# Both lists are APPEND-FRIENDLY — add a new shipped framework file here and to the
+# matching list in packages/mosaic/src/config/file-adapter.ts.
+FRAMEWORK_OWNED=("CONSTITUTION.md" "AGENTS.md" "STANDARDS.md")
+USER_SEEDED=("TOOLS.md")
 
 # Current framework schema version — bump this when the layout changes.
 # The migration system uses this to run upgrade steps.
-FRAMEWORK_VERSION=2
+FRAMEWORK_VERSION=3
 
 # ─── colours ──────────────────────────────────────────────────────────────────
 if [[ -t 1 ]]; then
@@ -40,6 +48,45 @@ warn() { echo -e "  ${YELLOW}⚠${RESET} $1" >&2; }
 fail() { echo -e "  ${RED}✗${RESET} $1" >&2; }
 step() { echo -e "\n${BOLD}$1${RESET}"; }
 
+# ─── snapshot / restore (crash safety for upgrades) ──────────────────────────
+SNAPSHOT_DIR=""
+make_snapshot() {
+  is_existing_install || return 0
+  SNAPSHOT_DIR="$(mktemp -d "${TMPDIR:-/tmp}/mosaic-snapshot-XXXXXX")"
+  cp -a "$TARGET_DIR/." "$SNAPSHOT_DIR/" 2>/dev/null || true
+}
+restore_snapshot() {
+  [[ -n "$SNAPSHOT_DIR" && -d "$SNAPSHOT_DIR" ]] || return 0
+  fail "Install interrupted/failed — restoring previous state from snapshot"
+  rm -rf "$TARGET_DIR"; mkdir -p "$TARGET_DIR"
+  cp -a "$SNAPSHOT_DIR/." "$TARGET_DIR/" 2>/dev/null || true
+}
+cleanup_snapshot() { [[ -n "$SNAPSHOT_DIR" && -d "$SNAPSHOT_DIR" ]] && rm -rf "$SNAPSHOT_DIR"; SNAPSHOT_DIR=""; }
+
+# Reconcile contract files after sync: framework-owned overwrite (backup-once),
+# user-seeded seed-if-absent.
+reconcile_framework_files() {
+  local defaults="$TARGET_DIR/defaults" f
+  [[ -d "$defaults" ]] || return 0
+  for f in "${FRAMEWORK_OWNED[@]}"; do
+    [[ -f "$defaults/$f" ]] || continue
+    if [[ -f "$TARGET_DIR/$f" ]] && ! cmp -s "$TARGET_DIR/$f" "$defaults/$f"; then
+      if [[ ! -f "$TARGET_DIR/${f}.pre-constitution.bak" ]]; then
+        cp "$TARGET_DIR/$f" "$TARGET_DIR/${f}.pre-constitution.bak"
+        warn "$f is now framework-owned and was updated; your previous copy is saved as ${f}.pre-constitution.bak — re-apply intended changes as a .local overlay or policy/ file (see CONSTITUTION.md / constitution/LAYER-MODEL.md)."
+      fi
+    fi
+    cp "$defaults/$f" "$TARGET_DIR/$f"
+  done
+  for f in "${USER_SEEDED[@]}"; do
+    [[ -f "$defaults/$f" ]] || continue
+    if [[ ! -f "$TARGET_DIR/$f" ]]; then
+      cp "$defaults/$f" "$TARGET_DIR/$f"
+      ok "Seeded $f from defaults"
+    fi
+  done
+}
+
 # ─── helpers ──────────────────────────────────────────────────────────────────
 
 is_existing_install() {
@@ -113,11 +160,14 @@ sync_framework() {
   fi
 
   if command -v rsync >/dev/null 2>&1; then
-    local rsync_args=(-a --delete --exclude ".git" --exclude ".framework-version")
+    local rsync_args=(-a --delete --exclude ".git" --exclude ".framework-version" --exclude "*.pre-constitution.bak")
 
     if [[ "$INSTALL_MODE" == "keep" ]]; then
+      # Anchor to the transfer root (leading /) so we preserve the TOP-LEVEL
+      # ~/.config/mosaic/<file> without also excluding defaults/<file> from sync
+      # (reconcile_framework_files needs the freshly-synced defaults/ copies).
       for path in "${PRESERVE_PATHS[@]}"; do
-        rsync_args+=(--exclude "$path")
+        rsync_args+=(--exclude "/$path")
       done
     fi
 
@@ -137,7 +187,7 @@ sync_framework() {
     done
   fi
 
-  find "$TARGET_DIR" -mindepth 1 -maxdepth 1 ! -name ".git" ! -name ".framework-version" -exec rm -rf {} +
+  find "$TARGET_DIR" -mindepth 1 -maxdepth 1 ! -name ".git" ! -name ".framework-version" ! -name "*.pre-constitution.bak" -exec rm -rf {} +
   cp -R "$SOURCE_DIR"/. "$TARGET_DIR"/
   rm -rf "$TARGET_DIR/.git"
 
@@ -195,10 +245,15 @@ run_migrations() {
     fi
   fi
 
-  # ── Future migrations go here ──────────────────────────────────────────────
-  # if [[ "$from_version" -lt 3 ]]; then
-  #   ...
-  # fi
+  # ── Migration: v2 → v3 (Constitution split) ───────────────────────────────
+  # CONSTITUTION.md / AGENTS.md / STANDARDS.md become framework-owned (overwritten
+  # on upgrade). reconcile_framework_files() has already run before this point: it
+  # backed up any user-edited copy to <file>.pre-constitution.bak and installed the
+  # new framework version. Nothing further to do here — the advisory was emitted at
+  # reconcile time. (STANDARDS.local.md composition lands with the overlay composer.)
+  if [[ "$from_version" -lt 3 ]]; then
+    ok "Migrated to the Constitution layout (framework-owned CONSTITUTION/AGENTS/STANDARDS)"
+  fi
 }
 
 # ═══════════════════════════════════════════════════════════════════════════════
@@ -216,6 +271,10 @@ else
   ok "Install mode: overwrite"
 fi
 
+# Snapshot before any destructive file operation; restore on interrupt/failure.
+make_snapshot
+trap 'restore_snapshot' ERR INT TERM
+
 sync_framework
 
 # Ensure persistent directories exist
@@ -230,15 +289,7 @@ mkdir -p "$TARGET_DIR/credentials"
 # packages/mosaic/src/config/file-adapter.ts (FileConfigAdapter.syncFramework).
 # SOUL.md and USER.md are intentionally NOT seeded here — they are generated
 # by `mosaic init` from templates with user-supplied values.
-DEFAULTS_DIR="$TARGET_DIR/defaults"
-if [[ -d "$DEFAULTS_DIR" ]]; then
-  for default_file in CONSTITUTION.md AGENTS.md STANDARDS.md TOOLS.md; do
-    if [[ -f "$DEFAULTS_DIR/$default_file" ]] && [[ ! -f "$TARGET_DIR/$default_file" ]]; then
-      cp "$DEFAULTS_DIR/$default_file" "$TARGET_DIR/$default_file"
-      ok "Seeded $default_file from defaults"
-    fi
-  done
-fi
+reconcile_framework_files
 
 # Ensure tool scripts are executable
 find "$TARGET_DIR/tools" -name "*.sh" -exec chmod +x {} + 2>/dev/null || true
@@ -249,6 +300,18 @@ ok "Framework synced to $TARGET_DIR"
 # Run migrations before post-install (migrations may remove old bin/ etc.)
 run_migrations
 
+# File-system phase complete and consistent — clear the restore trap.
+trap - ERR INT TERM
+cleanup_snapshot
+
+# Testability / minimal-install hook: stop after the file-system phase, before any
+# environment-touching post-install steps (runtime linking, MCP setup, skills, doctor).
+if [[ "${MOSAIC_SYNC_ONLY:-0}" == "1" ]]; then
+  write_framework_version
+  ok "Sync-only mode: file phase complete"
+  exit 0
+fi
+
 step "Post-install tasks"
 
 SCRIPTS="$TARGET_DIR/tools/_scripts"