feat: add SQLite FTS storage backend

.agents/skills/complex-dev/SKILL.md

@@ -0,0 +1,43 @@
+---
+name: complex-dev
+description: Execute complex programming tasks with a rigorous, zero-compromise workflow. Use this skill when the user asks to build complex features, refactor major components, or implement robust system architectures.
+---
+
+# Complex Development Workflow
+
+You are an expert software engineer executing complex programming tasks. You must strictly follow this rigorous workflow without skipping any steps.
+
+## 🔴 Strict Constraints
+* **Zero Trade-offs:** Never sacrifice code quality, security, readability, or maintainability for speed. Do not use hacky workarounds or leave critical "TODO" comments.
+* **CLAUDE.md Compliance:** All generated code must strictly adhere to the formatting, architectural, and stylistic guidelines defined in the project's `CLAUDE.md` file.
+
+---
+
+## Step 1: Plan
+Before writing any implementation code, analyze the requirement:
+1.  Outline the system architecture, data flow, and necessary components.
+2.  Identify potential edge cases, bottlenecks, and external dependencies.
+3.  Draft a brief step-by-step execution plan and explicitly state it.
+
+## Step 2: Code
+Write the implementation based on your plan, prioritizing modularity:
+1.  **Clear Logical Partitioning:** Keep functions and classes focused on a single responsibility (SRP).
+2.  **File Splitting:** Do not dump unrelated logic into a monolithic file. Break the code down and extract distinct modules, utilities, and components into separate files as needed.
+3.  Ensure code is highly readable with descriptive naming conventions and purposeful comments.
+
+## Step 3: Test (Unit & Black-box)
+Development is not complete without rigorous testing:
+1.  **Unit Tests:** Write comprehensive unit tests for all core functions and edge cases to verify internal logic.
+2.  **Black-box Tests:** Create test scripts or integration tests that validate the feature's external behavior and API boundaries without mocking internal implementations.
+
+## Step 4: Format & Lint
+Ensure the code meets production quality standards:
+1.  Run the project's designated code formatter.
+2.  Run the project's linter.
+3.  Automatically fix **all** linting errors and warnings. The code must be completely clean.
+
+## Step 5: Verify
+Finalize the task with end-to-end validation:
+1.  Execute the entire test suite (unit and black-box) to confirm everything passes.
+2.  Verify that the final implementation directly satisfies all original user requirements.
+3.  Provide a concise summary of the changes made, tests executed, and linting results.

.github/workflows/ci.yml

@@ -43,14 +43,23 @@ jobs:
       - name: Check workspace
         run: cargo check --locked --workspace --all-targets
 
+      - name: Check SQLite feature set
+        run: cargo check --locked --no-default-features --features sqlite-fts --workspace --all-targets
+
       - name: Run Clippy
         run: cargo clippy --locked --workspace --all-targets -- -D warnings
 
+      - name: Run Clippy for SQLite
+        run: cargo clippy --locked --no-default-features --features sqlite-fts --workspace --all-targets -- -D warnings
+
       - name: Run unit tests
         run: cargo test --locked --workspace
 
+      - name: Run SQLite unit tests
+        run: cargo test --locked --no-default-features --features sqlite-fts --workspace
+
   blackbox:
-    name: PostgreSQL black-box
+    name: Storage black-box
     runs-on: ubuntu-latest
     steps:
       - name: Checkout

CLAUDE.md

@@ -1,8 +1,8 @@
 # abyss-backend Development Guide
 
 `abyss-backend` is the standalone open-source Agent event service. It owns
-event ingestion, PostgreSQL persistence, event queries, optional Elasticsearch
-projection, and the HTTP API that exposes those capabilities.
+event ingestion, compile-time-selected persistence and search, event queries,
+and the HTTP API that exposes those capabilities.
 
 Keep the repository focused on these public event-service responsibilities.
 
@@ -11,9 +11,11 @@ Keep the repository focused on these public event-service responsibilities.
 - `api` owns HTTP routing and response boundaries.
 - `identity` validates the deployment bearer token and returns the stable
   standalone owner identifier.
-- `usage` owns event request types, validation, ingestion, and queries.
-- `search` owns the Elasticsearch projection and search worker.
-- `db` owns PostgreSQL pooling, the consolidated migration, and Diesel models.
+- `usage` owns event contracts plus backend-independent validation and ordering.
+- `search` owns shared search contracts and safe projection extraction.
+- `storage` is the `dyn StorageBackend` compatibility boundary and contains the
+  conditionally compiled PostgreSQL/Elasticsearch and SQLite/FTS5 backends.
+- `db` owns PostgreSQL-only pooling, migrations, and Diesel models.
 
 Keep modules focused and start new Rust module files with a `//!` responsibility
 comment. Keep the implementation self-contained within this repository.
@@ -23,6 +25,8 @@ comment. Keep the implementation self-contained within this repository.
 ```bash
 cargo +nightly fmt --all -- --check
 cargo clippy --workspace --all-targets -- -D warnings
+cargo clippy --no-default-features --features sqlite-fts --workspace --all-targets -- -D warnings
 cargo test --workspace
+cargo test --no-default-features --features sqlite-fts --workspace
 make test-blackbox
 ```

Makefile

@@ -1,4 +1,4 @@
-.PHONY: check fmt clippy test test-blackbox docker-build k8s-render
+.PHONY: check fmt clippy test test-blackbox test-blackbox-postgres test-blackbox-sqlite docker-build k8s-render
 
 check: fmt clippy test
 
@@ -7,13 +7,20 @@ fmt:
 
 clippy:
 	cargo clippy --locked --workspace --all-targets -- -D warnings
+	cargo clippy --locked --no-default-features --features sqlite-fts --workspace --all-targets -- -D warnings
 
 test:
 	cargo test --locked --workspace
+	cargo test --locked --no-default-features --features sqlite-fts --workspace
 
-test-blackbox:
+test-blackbox: test-blackbox-postgres test-blackbox-sqlite
+
+test-blackbox-postgres:
 	bash scripts/blackbox_abyss_backend.sh
 
+test-blackbox-sqlite:
+	bash scripts/blackbox_sqlite_backend.sh
+
 docker-build:
 	docker build -t abyss-backend:local .