diff --git a/.github/scripts/check_migration_idempotency.py b/.github/scripts/check_migration_idempotency.py
new file mode 100644
index 00000000..5c6606b6
--- /dev/null
+++ b/.github/scripts/check_migration_idempotency.py
@@ -0,0 +1,89 @@
+#!/usr/bin/env python3
+"""Fail CI on non-idempotent raw index SQL in EF migrations.
+
+EF applies migrations at startup on Render; a raw CREATE INDEX for an index that
+already exists throws Postgres 42P07 and fails the deploy. Every raw CREATE INDEX
+inside migrationBuilder.Sql(...) must carry IF NOT EXISTS, and every raw DROP
+INDEX must carry IF EXISTS. The fluent migrationBuilder.CreateIndex(...) /
+DropIndex(...) API is already idempotent-safe and is not flagged (its method
+names carry no whitespace, so they never match the raw-SQL patterns).
+
+Mirrors checkEfMigrationRawIndex in the orbit-ui-mobile consumer repo
+(.claude/hooks/_lib/rules-source.mjs): only the balanced-paren body of each
+migrationBuilder.Sql(...) call is scanned, split into ;-separated statements so
+one statement's IF [NOT] EXISTS clause cannot mask a sibling that lacks its own.
+
+    check_migration_idempotency.py <migration.cs> [<migration.cs> ...]
+"""
+import os
+import re
+import sys
+
+SQL_CALL = re.compile(r"migrationBuilder\.Sql\s*\(")
+CREATE_INDEX = re.compile(r"\bCREATE\s+(?:UNIQUE\s+)?INDEX\b", re.IGNORECASE)
+IF_NOT_EXISTS = re.compile(r"\bIF\s+NOT\s+EXISTS\b", re.IGNORECASE)
+DROP_INDEX = re.compile(r"\bDROP\s+INDEX\b", re.IGNORECASE)
+IF_EXISTS = re.compile(r"\bIF\s+EXISTS\b", re.IGNORECASE)
+
+
+def find_violations(path: str, contents: str) -> list[str]:
+    """Return one message per non-idempotent raw index statement in the file."""
+    findings: list[str] = []
+    for call in SQL_CALL.finditer(contents):
+        index = call.end()
+        depth = 1
+        start = index
+        while index < len(contents) and depth > 0:
+            char = contents[index]
+            if char == "(":
+                depth += 1
+            elif char == ")":
+                depth -= 1
+            index += 1
+        sql = contents[start : index - 1]
+        line_number = contents.count("\n", 0, call.start()) + 1
+        for statement in sql.split(";"):
+            if CREATE_INDEX.search(statement) and not IF_NOT_EXISTS.search(statement):
+                findings.append(f"{path}:{line_number} raw CREATE INDEX without IF NOT EXISTS")
+            if DROP_INDEX.search(statement) and not IF_EXISTS.search(statement):
+                findings.append(f"{path}:{line_number} raw DROP INDEX without IF EXISTS")
+    return findings
+
+
+def _confine(candidate: str, base: str) -> str:
+    """Resolve candidate and confirm it stays within base, rejecting path traversal."""
+    resolved = os.path.realpath(candidate)
+    if resolved != base and not resolved.startswith(base + os.sep):
+        raise ValueError(f"Refusing path outside {base}: {candidate}")
+    return resolved
+
+
+def main() -> int:
+    base = os.path.realpath(os.getcwd())
+    violations: list[str] = []
+    for path in sys.argv[1:]:
+        try:
+            safe_path = _confine(path, base)
+        except ValueError as error:
+            print(error, file=sys.stderr)
+            continue
+        try:
+            with open(safe_path, encoding="utf-8") as handle:
+                contents = handle.read()
+        except (OSError, UnicodeDecodeError) as error:
+            print(f"Skipping unreadable file {path}: {error}", file=sys.stderr)
+            continue
+        violations.extend(find_violations(path, contents))
+
+    if violations:
+        print("::error::Non-idempotent raw index SQL in EF migration(s). Use CREATE INDEX IF NOT EXISTS / DROP INDEX IF EXISTS so a startup re-apply cannot throw Postgres 42P07 and fail the Render deploy.")
+        for violation in violations:
+            print(violation)
+        return 1
+
+    print("OK: no non-idempotent raw index SQL in the checked migrations.")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index db68aa8d..a0f44e1e 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -113,6 +113,16 @@ jobs:
           fi
           echo "OK: no existing migration was edited (new migrations are allowed)."
 
+      - name: Fail on non-idempotent raw index SQL in new migrations
+        env:
+          BASE_REF: ${{ github.base_ref }}
+        run: |
+          git fetch origin "$BASE_REF"
+          echo "Changed migration files:"
+          git diff --name-only --diff-filter=d "origin/$BASE_REF...HEAD" -- ':(glob)**/Migrations/*.cs'
+          git diff --name-only -z --diff-filter=d "origin/$BASE_REF...HEAD" -- ':(glob)**/Migrations/*.cs' \
+            | xargs -0 --no-run-if-empty python3 .github/scripts/check_migration_idempotency.py
+
   convention-guard:
     name: Guard Conventions
     runs-on: ubuntu-latest
diff --git a/AGENTS.md b/AGENTS.md
index f462986c..65bbb2b3 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -21,6 +21,25 @@ CLAUDE.md; this file holds the worker contract and the review rules and DEFERS t
 - DTO/contract changes are append-only and deploy-API-first; the TypeScript consumer
   (orbit-ui-mobile) updates in lockstep via its own ticket that this one blocks.
 
+### Guardrails you must not trip
+
+These hold for EVERY worker and every engine. They are enforced by CI, GitHub branch
+protection, and the lefthook pre-commit/pre-push hooks, NOT by the Claude Code session
+hooks (those do not run under `codex exec` or a raw shell). This list is the readable
+copy; the gates are the enforcement.
+
+- Never push or force-push to `main`/`master`. Branch to `feature/`|`fix/`|`chore/`,
+  open a PR, squash-merge only. Never reuse a squash-merged branch.
+- Never bypass the git hooks: no `--no-verify` (or its `-n` commit alias), no
+  `--no-gpg-sign` and no `commit.gpgsign=false`. Fix what a hook flags, then commit.
+- Never `git worktree remove --force`: on Windows it follows a junction and deletes the
+  link target. Remove the junctions first, then remove the worktree without `--force`.
+- EF migrations must be idempotent: raw `CREATE INDEX` inside `migrationBuilder.Sql(...)`
+  needs `IF NOT EXISTS`, and raw `DROP INDEX` needs `IF EXISTS` (EF re-applies at startup
+  on Render; a duplicate raw `CREATE INDEX` throws Postgres 42P07 and fails the deploy).
+  The fluent `migrationBuilder.CreateIndex(...)`/`DropIndex(...)` API is already safe.
+  The Guard Migrations CI job enforces this over changed `Migrations/*.cs` files.
+
 ## Code Review Rules
 
 Only what no gate can check; mechanical findings belong to CI. Flag P0/P1 only.
diff --git a/lefthook.yml b/lefthook.yml
index f0c90b97..8fbc38ff 100644
--- a/lefthook.yml
+++ b/lefthook.yml
@@ -7,3 +7,18 @@ pre-commit:
       stage_fixed: true
     dashes:
       run: node tools/check-dashes.mjs --files {staged_files}
+pre-push:
+  commands:
+    protect-main:
+      use_stdin: true
+      run: |
+        blocked=0
+        while read -r _local_ref _local_sha remote_ref _remote_sha; do
+          case "$remote_ref" in
+            refs/heads/main|refs/heads/master) blocked=1 ;;
+          esac
+        done
+        if [ "$blocked" -eq 1 ]; then
+          echo "BLOCKED: pushing to main/master is forbidden (branch protection, squash-merge only). Open a PR."
+          exit 1
+        fi