knowledge: agent self-correction with audit + per-persona gate + revert

Bundles three coupled changes so agent-side mutations stay
auditable and reversible:

1. Audit columns on entity_facts —
   `last_modified_by_model` / `last_modified_by_backend` /
   `last_modified_at`. Stamped on every mutation path
   (update_fact, supersede_fact, manual PATCH, manual supersede,
   the new revert). NULL on rows never touched since creation.
   Partial index on `last_modified_at WHERE NOT NULL` keeps the
   "show me recent edits" feed fast without bloating from legacy
   rows.

2. Per-persona gate `personas.allow_agent_corrections` (BOOLEAN,
   default 0). Defense in depth at two layers:
   - build_tool_definitions: when off, `update_fact` and
     `supersede_fact` aren't in the catalog at all, so even a
     hallucinated tool call by the model fails fast.
   - tool_update_fact / tool_supersede_fact: re-checks the persona
     flag at call time and returns an explicit "corrections
     disabled" error if it's somehow off (e.g. flag flipped mid-
     loop).
   ToolGateOpts grows the flag; current_gate_opts splits into
   `current_gate_opts` (no persona context, defaults closed) +
   `current_gate_opts_for_persona` for chat callers that have a
   persona id. Both call sites in insight_chat are updated.

3. Revert action — new DAO method `revert_supersession` +
   `POST /knowledge/facts/{id}/restore`. Flips status back to
   'active', clears `superseded_by`, clears `valid_until` (we
   don't track whether it was hand-set vs auto-stamped, so the
   safe reset is to drop it — user can re-bound after). Stamps
   `last_modified_*` so the revert itself is attributable.

Manual paths (PATCH / supersede via HTTP, plus restore) stamp the
audit columns with `("manual", "manual")`. Agent paths stamp the
loop-time chat model and backend (mirroring the existing
created_by_* convention).

FactDetail in the HTTP response now carries the audit triple
alongside the existing provenance. Apollo wires the new field set
in the matching commit.

PersonaView / UpdatePersonaRequest grow `allowAgentCorrections`;
the PersonaPatch + InsertPersona + bulk_import paths thread it.

317 lib tests pass, including unchanged update_fact / supersede
DAO tests (now passing audit=None — None means "no provenance
context to attribute", legacy semantics).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/database/persona_dao.rs

@@ -18,6 +18,7 @@ pub struct PersonaPatch {
     pub system_prompt: Option<String>,
     pub include_all_memories: Option<bool>,
     pub reviewed_only_facts: Option<bool>,
+    pub allow_agent_corrections: Option<bool>,
 }
 
 /// One row of a bulk migration upload. Fields named to match the JSON
@@ -166,6 +167,7 @@ impl PersonaDao for SqlitePersonaDao {
                     created_at: now,
                     updated_at: now,
                     reviewed_only_facts: false,
+                    allow_agent_corrections: false,
                 })
                 .execute(conn.deref_mut())
                 .map_err(|e| anyhow::anyhow!("Insert error: {}", e))?;
@@ -222,6 +224,15 @@ impl PersonaDao for SqlitePersonaDao {
                     .execute(conn.deref_mut())
                     .map_err(|e| anyhow::anyhow!("Update reviewed_only_facts error: {}", e))?;
             }
+            if let Some(new_allow_corrections) = patch.allow_agent_corrections {
+                diesel::update(personas.filter(user_id.eq(uid)).filter(persona_id.eq(pid)))
+                    .set((
+                        allow_agent_corrections.eq(new_allow_corrections),
+                        updated_at.eq(now),
+                    ))
+                    .execute(conn.deref_mut())
+                    .map_err(|e| anyhow::anyhow!("Update allow_agent_corrections error: {}", e))?;
+            }
 
             personas
                 .filter(user_id.eq(uid))
@@ -396,6 +407,7 @@ mod tests {
                     system_prompt: Some("new prompt".into()),
                     include_all_memories: None,
                     reviewed_only_facts: None,
+                    allow_agent_corrections: None,
                 },
             )
             .unwrap()
@@ -425,6 +437,7 @@ mod tests {
                     system_prompt: None,
                     include_all_memories: Some(true),
                     reviewed_only_facts: None,
+                    allow_agent_corrections: None,
                 },
             )
             .unwrap()