Add duplicate entry prevention to LLM tool pipeline

Three-layer guard on create_note and create_task:
1. Exact title match (get_note_by_title, case-insensitive) → hard block,
   redirects model to use update_note instead
2. Fuzzy title match (SequenceMatcher ≥82%, punct-stripped word search for
   candidates) → hard block; catches "Game Premise" vs "Game Premise Notes"
3. Semantic content similarity (semantic_search_notes threshold=0.87) → soft
   block with requires_confirmation:true; model asks user then retries with
   confirmed:true; graceful no-op if embedding model is unavailable

create_project and create_milestone now always require confirmed:true before
creation (structural entities — must be intentional). Both are also guarded
by exact + fuzzy title checks post-confirmation.

create_note and create_task gain an optional confirmed parameter (not
required by default; only used to bypass a content-similarity soft-block
after the user has been asked).

Helpers added to tools.py:
- _fuzzy_title_match(title, candidates, threshold=0.82)
- _PUNCT_RE for stripping punctuation before word-search candidate fetch
- difflib.SequenceMatcher and re imported at module level

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

summary.md

@@ -12,7 +12,7 @@
 >    Include file-level details in the commit body when the change is non-trivial.
 
 ## Last Updated
-2026-03-03 — Project/milestone association bug fixes (tasks route was silently dropping project_id/milestone_id); PATCH /api/notes endpoint; parent_title in task API response; milestone_id support in NoteEditorView + notes store; sub-tasks inherit milestone; list_notes OR query for project view; AppHeader redesigned (centered nav, gear dropdown for settings)
+2026-03-03 — Duplicate entry prevention in LLM tool pipeline: exact-title block, fuzzy-title block (SequenceMatcher ≥82%), semantic content check (≥87% cosine similarity via existing `semantic_search_notes`); `create_project`/`create_milestone` require explicit `confirmed:true`; `create_note`/`create_task` have optional `confirmed` for content-similarity soft-block; `create_project`/`create_milestone` also protected by exact+fuzzy title checks
 
 ## Project Overview
 Fabled Assistant is a self-hosted note-taking and task-tracking application with
@@ -612,7 +612,15 @@ When adding a new migration, follow these conventions:
   System prompt includes today's date for relative date resolution. Graceful degradation: models without
   tool support respond normally.
   Full tool suite:
-  - `create_task` / `create_note` — create new items
+  - `create_task` / `create_note` — create new items; protected by a three-layer duplicate guard:
+    1. **Exact title** (case-insensitive via `get_note_by_title`) → hard block, redirect to `update_note`
+    2. **Fuzzy title** (`SequenceMatcher` ≥82%; strips punctuation before word search for candidates) → hard block
+    3. **Semantic content** (`semantic_search_notes` threshold 0.87, graceful no-op if embedding model down) → soft block with `requires_confirmation:true`; model must ask user then retry with `confirmed:true`
+    Both tools have an optional `confirmed` parameter (not required by default — only needed when a content-similarity warning fires).
+  - `create_project` — always requires `confirmed:true` before creation (structural, must be intentional);
+    additionally guarded by exact + fuzzy title checks (≥82%) against existing projects
+  - `create_milestone` — always requires `confirmed:true`; additionally guarded by exact + fuzzy title
+    checks against existing milestones within the same project
   - `update_note` — edit note content (replace/append) AND update task fields: `status`, `priority`,
     `due_date`, `tags` (with `tag_mode`: replace/add/remove); finds by exact title first, falls back to fuzzy search
   - `delete_note` / `delete_task` — permanently delete (require user confirmation via confirm UI;
@@ -625,6 +633,7 @@ When adding a new migration, follow these conventions:
   - Full CalDAV suite: `create_event`, `list_events`, `search_events`, `update_event`, `delete_event`,
     `list_calendars`, `create_todo`, `list_todos`, `search_todos`, `update_todo`, `complete_todo`, `delete_todo`
     (`search_todos` keyword-filters the todo list — companion to `list_todos`)
+  - **Duplicate guard helpers** in `services/tools.py`: `_fuzzy_title_match(title, candidates, threshold=0.82)` uses `SequenceMatcher`; semantic check uses `semantic_search_notes` at threshold 0.87 (vs. 0.45 for RAG suggestions). `_PUNCT_RE` strips punctuation from title before word-search to avoid false-negative candidates (e.g. "Shackled - Game Premise" → "Shackled Game Premise" query).
 - **Streaming status transparency:** The backend emits `status` SSE events at each pipeline stage
   so the user always sees what's happening instead of a blank progress dot. Stages:
   (1) intent ack text streamed as a `chunk` event (tool responses — TTFT ~400ms) or