feat(registration): write CLAUDE.custodian.md instead of overwriting CLAUDE.md

Instead of overwriting the target repo's CLAUDE.md, the registration
script now writes CLAUDE.custodian.md — a suggestion file with an
integration header. The repo's Claude agent integrates both files and
deletes the suggestion when done, preserving existing project conventions.

Also fix: `read` prompt now redirects from /dev/tty so the script
doesn't exit with code 1 when run non-interactively via make.

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

scripts/register_project.sh

@@ -15,7 +15,7 @@
 #   2. Verify the domain exists via GET /domains/{slug}/
 #   3. Look up the topic ID for the domain (first active topic)
 #   4. Check that state-hub is in ~/.claude.json; warn if missing
-#   5. Write $project_path/CLAUDE.md from the template (skip if exists or --additional)
+#   5. Write $project_path/CLAUDE.custodian.md (suggestion; repo agent integrates → CLAUDE.md)
 #   6. POST to /repos/ to register the repo
 #   7. POST a progress event recording the registration
 
@@ -112,24 +112,39 @@ else
     echo "    MCP OK"
 fi
 
-# ── Step 5: Write CLAUDE.md ────────────────────────────────────────────────────
+# ── Step 5: Write CLAUDE.custodian.md (suggestion for the repo agent) ─────────
 CLAUDE_MD="$PROJECT_PATH/CLAUDE.md"
+SUGGESTION_FILE="$PROJECT_PATH/CLAUDE.custodian.md"
 TEMPLATE="$SCRIPT_DIR/project_claude_md.template"
 
-if [[ "$ADDITIONAL" == "--additional" ]]; then
-    echo "==> --additional flag: skipping CLAUDE.md (already exists for this domain)."
-elif [[ -f "$CLAUDE_MD" ]]; then
-    echo "==> CLAUDE.md already exists at $CLAUDE_MD — skipping."
-else
-    echo "==> Writing CLAUDE.md to $CLAUDE_MD ..."
+echo "==> Writing custodian suggestion to $SUGGESTION_FILE ..."
+{
+    cat <<'PREAMBLE'
+<!--
+  CUSTODIAN SUGGESTION — generated by `make register-project`
+
+  This file was written by the Custodian State Hub registration workflow.
+  It contains the standard State Hub integration block for this repository.
+
+  A Claude Code agent in this repo should:
+    1. Read this file and the existing CLAUDE.md side by side
+    2. Integrate the sections below into CLAUDE.md — preserve all existing
+       project-specific conventions; add or update the hub integration block
+    3. Delete this file once integration is complete and commit the result
+
+  Do NOT add this file to .gitignore. It is a temporary artefact that signals
+  pending integration work to the repo agent.
+-->
+
+PREAMBLE
     sed \
         -e "s|{PROJECT_NAME}|$PROJECT_NAME|g" \
         -e "s|{DOMAIN}|$DOMAIN|g" \
         -e "s|{TOPIC_ID}|$TOPIC_ID|g" \
         -e "s|{REPO_SLUG}|$REPO_SLUG|g" \
-        "$TEMPLATE" > "$CLAUDE_MD"
-    echo "    Written."
-fi
+        "$TEMPLATE"
+} > "$SUGGESTION_FILE"
+echo "    Written. The repo agent should integrate it into CLAUDE.md and delete this file."
 
 # ── Step 6: Register repo in State Hub ────────────────────────────────────────
 echo "==> Registering repo '$PROJECT_NAME' under domain '$DOMAIN' ..."
@@ -165,7 +180,7 @@ payload = {
     'author': 'custodian',
     'detail': {
         'project_path': '$PROJECT_PATH',
-        'claude_md': '$CLAUDE_MD',
+        'suggestion_file': '$SUGGESTION_FILE',
         'domain': '$DOMAIN',
         'repo_slug': '$REPO_SLUG',
     },
@@ -184,14 +199,14 @@ echo "  Project:   $PROJECT_NAME"
 echo "  Domain:    $DOMAIN"
 echo "  Repo slug: $REPO_SLUG"
 [[ -n "$TOPIC_ID" ]] && echo "  Topic ID:  $TOPIC_ID"
-echo "  CLAUDE.md: $CLAUDE_MD"
+echo "  Suggestion: $SUGGESTION_FILE  (repo agent should integrate → CLAUDE.md)"
 echo ""
 echo "Next: restart Claude Code for the MCP server to be available in this project."
 
 # ── Optional: SBOM ingest ─────────────────────────────────────────────────────
 if [[ "$ADDITIONAL" != "--additional" ]]; then
     echo ""
-    read -r -p "==> Run SBOM ingest now? (auto-detects lockfile in $PROJECT_PATH) [y/N] " INGEST_NOW
+    read -r -p "==> Run SBOM ingest now? (auto-detects lockfile in $PROJECT_PATH) [y/N] " INGEST_NOW </dev/tty || INGEST_NOW="N"
     if [[ "$INGEST_NOW" =~ ^[Yy]$ ]]; then
         echo "==> Ingesting SBOM for '$REPO_SLUG' ..."
         INGEST_UV="$STATE_HUB_DIR/.venv/bin/python"