fix(installer): preserve credentials dir and seed STANDARDS.md on install

- Add credentials/ to PRESERVE_PATHS so rsync --delete doesn't wipe
  user credential stores on framework upgrades
- Add AGENTS.md and STANDARDS.md to PRESERVE_PATHS to protect
  user-customized copies from being deleted during sync
- Seed AGENTS.md and STANDARDS.md from defaults/ on first install
  (previously only existed in defaults/ but never copied to framework root)
- Create credentials/ directory during install (alongside memory/)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/mosaic/framework/install.sh

@@ -19,8 +19,9 @@ SOURCE_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 TARGET_DIR="${MOSAIC_HOME:-$HOME/.config/mosaic}"
 INSTALL_MODE="${MOSAIC_INSTALL_MODE:-prompt}"
 
-# Files preserved across upgrades (never overwritten)
-PRESERVE_PATHS=("SOUL.md" "USER.md" "TOOLS.md" "memory" "sources")
+# 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")
 
 # Current framework schema version — bump this when the layout changes.
 # The migration system uses this to run upgrade steps.
@@ -217,8 +218,22 @@ fi
 
 sync_framework
 
-# Ensure memory directory exists
+# Ensure persistent directories exist
 mkdir -p "$TARGET_DIR/memory"
+mkdir -p "$TARGET_DIR/credentials"
+
+# Seed defaults — copy from defaults/ to framework root if not already present.
+# These are user-editable files that ship with sensible defaults but should
+# never be overwritten once the user has customized them.
+DEFAULTS_DIR="$TARGET_DIR/defaults"
+if [[ -d "$DEFAULTS_DIR" ]]; then
+  for default_file in AGENTS.md STANDARDS.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
 
 # Ensure tool scripts are executable
 find "$TARGET_DIR/tools" -name "*.sh" -exec chmod +x {} + 2>/dev/null || true