Add fail_count and last_failed_at to kb_documents

Simplified KB indexing state tracking - added columns directly
to kb_documents instead of separate table. This enables per-file
backoff retry logic.

migrations/6.1.8-01-research/up.sql

@@ -11,6 +11,8 @@ CREATE TABLE IF NOT EXISTS kb_documents (
     first_published_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
     last_modified_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
     indexed_at TIMESTAMPTZ,
+    fail_count INT NOT NULL DEFAULT 0,
+    last_failed_at TIMESTAMPTZ,
     metadata JSONB DEFAULT '{}'::jsonb,
     created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
     updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
@@ -21,6 +23,7 @@ CREATE INDEX IF NOT EXISTS idx_kb_documents_bot_id ON kb_documents(bot_id);
 CREATE INDEX IF NOT EXISTS idx_kb_documents_collection ON kb_documents(collection_name);
 CREATE INDEX IF NOT EXISTS idx_kb_documents_hash ON kb_documents(file_hash);
 CREATE INDEX IF NOT EXISTS idx_kb_documents_indexed_at ON kb_documents(indexed_at);
+CREATE INDEX IF NOT EXISTS idx_kb_documents_fail ON kb_documents(bot_id, collection_name, fail_count) WHERE fail_count > 0;
 
 -- Knowledge Base Collections
 CREATE TABLE IF NOT EXISTS kb_collections (

src/core/shared/schema/research.rs

@@ -12,6 +12,8 @@ diesel::table! {
         first_published_at -> Timestamptz,
         last_modified_at -> Timestamptz,
         indexed_at -> Nullable<Timestamptz>,
+        fail_count -> Int4,
+        last_failed_at -> Nullable<Timestamptz>,
         metadata -> Nullable<Jsonb>,
         created_at -> Timestamptz,
         updated_at -> Timestamptz,
@@ -171,3 +173,17 @@ diesel::joinable!(research_findings -> research_projects (project_id));
 diesel::joinable!(research_citations -> research_sources (source_id));
 diesel::joinable!(research_collaborators -> research_projects (project_id));
 diesel::joinable!(research_exports -> research_projects (project_id));
+
+diesel::allow_tables_to_appear_in_same_query!(
+    kb_documents,
+    kb_collections,
+    kb_group_associations,
+    user_kb_associations,
+    research_projects,
+    research_sources,
+    research_notes,
+    research_findings,
+    research_citations,
+    research_collaborators,
+    research_exports,
+);

src/drive/drive_monitor/mod.rs

@@ -565,10 +565,19 @@ impl DriveMonitor {
                 file_states.remove(&path);
             }
         }
-        for (path, mut state) in current_files {
+        for (path, new_state) in current_files {
+            let mut state = new_state;
             if path.ends_with(".bas") {
                 state.indexed = true;
             }
+            // Preserve fail_count and last_failed_at for existing files that weren't modified
+            if let Some(prev_state) = file_states.get(&path) {
+                if prev_state.etag == state.etag {
+                    // File wasn't modified - preserve fail_count and last_failed_at
+                    state.fail_count = prev_state.fail_count;
+                    state.last_failed_at = prev_state.last_failed_at;
+                }
+            }
             file_states.insert(path, state);
         }
         // Save file states to disk in background to avoid blocking