refactor(util): make render_diff generic (caller supplies side titles); move to root util

Generalize render_diff so it isn't supervise-flavored: the "(current)" /
"(proposed)" side titles are no longer baked in — callers pass `before_title`
and `after_label` (required). Move it from orchestrator/supervisor/util.py to
the base bot_bottle.util alongside sha256_hex, and delete the now-empty
supervisor/util.py.

The supervise callsite (Orchestrator.supervise_respond) assigns
before_title="current", after_label="proposed"; the facade no longer re-exports
render_diff (callers import from bot_bottle.util). Behavior at the supervise
callsite is unchanged.

Full unit suite green (2243).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/orchestrator/supervisor/__init__.py

@@ -7,9 +7,10 @@ object — optionally scoped to a `db_path` — makes the orchestrator's supervi
 dependency explicit and injectable in tests.
 
 For convenience this package also re-exports the neutral vocabulary
-(`bot_bottle.supervisor`'s types + `SupervisePlan`) and the pure `render_diff`
-helper (`util`), so orchestrator-side callers import from one place. The data
-plane must NOT import this package — it imports
+(`bot_bottle.supervisor`'s types + `SupervisePlan`), so orchestrator-side
+callers import from one place. (Generic helpers like `render_diff` /
+`sha256_hex` live in `bot_bottle.util`.) The data plane must NOT import this
+package — it imports
 `bot_bottle.supervisor` (neutral) directly and reaches the queue over the
 control-plane RPC.
 """
@@ -24,7 +25,6 @@ from ..store.store_manager import StoreManager
 from ..store.queue_store import QueueStore
 from ...store.audit_store import AuditStore
 from ...supervisor.types import AuditEntry, Proposal, Response
-from .util import render_diff  # noqa: F401 — re-exported for callers
 
 
 class Supervisor:

bot_bottle/orchestrator/supervisor/util.py

@@ -1,26 +0,0 @@
-"""Pure supervise helpers — diff rendering.
-
-Stateless utility used alongside the `Supervisor` service. Kept as a plain
-function (not a method) because it carries no state. (Content hashing is a
-generic helper — `bot_bottle.util.sha256_hex`.)
-"""
-
-from __future__ import annotations
-
-import difflib
-
-
-def render_diff(before: str, after: str, *, label: str = "config") -> str:
-    """Unified diff suitable for the audit log + TUI. Empty diff (no changes)
-    renders as the empty string."""
-    diff = difflib.unified_diff(
-        before.splitlines(keepends=True),
-        after.splitlines(keepends=True),
-        fromfile=f"{label} (current)",
-        tofile=f"{label} (proposed)",
-        lineterm="",
-    )
-    parts = list(diff)
-    if not parts:
-        return ""
-    return "".join(p if p.endswith("\n") else p + "\n" for p in parts).rstrip("\n")