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+# SQLite Store and Web App Design
+
+## Goal
+
+Move Newsletter Link Catalog from spreadsheet-first output to a SQLite-first local catalog, while preserving spreadsheet output as an optional export/sync path. Add a functional local web app for browsing the catalog.
+
+## Scope
+
+This first pass keeps the working CLI ingestion flow. `nlc run` continues to fetch Gmail newsletters, parse links, categorize, enrich when enabled, and update incremental state. The main behavior change is that extracted data is persisted to SQLite by default.
+
+The web app is intentionally plain and functional. It should make the catalog useful before investing in visual polish.
+
+## Architecture
+
+Add a persistence layer alongside the existing output writers:
+
+- `DatabaseWriter` persists run results into SQLite.
+- Spreadsheet writers remain available through the existing config-driven write path during `nlc run`.
+- Web routes read from SQLite and do not re-run Gmail ingestion.
+- Existing parsing, filtering, categorization, enrichment, state, and OAuth modules stay in place.
+
+The CLI remains the control surface for ingestion:
+
+- `nlc run` writes to SQLite by default.
+- `nlc run` may also write Excel and/or Google Sheets if configured.
+- `nlc serve` starts a local web server against the configured SQLite database.
+
+## SQLite Database
+
+Default database path: `./data/newsletter-catalog.sqlite`, configurable as `database.path`.
+
+Tables:
+
+- `newsletters`: newsletter identity and display name.
+- `issues`: one row per processed email issue, linked to a newsletter.
+- `links`: canonical URL-level records.
+- `link_occurrences`: per-issue link appearances, including category, title, description, page metadata, and also-in text.
+- `sponsors`: sponsor/ad appearances, linked to issue and URL where possible.
+- `dead_links`: dead or unreachable link records.
+- `runs`: import run history with counts, timestamps, mode, and error counts.
+
+Constraints:
+
+- URLs are deduplicated in `links` by normalized URL.
+- Link occurrences are deduplicated per issue by normalized URL.
+- Processed Gmail message IDs remain tracked by the existing state file for now, avoiding a risky migration in this first pass.
+
+## Configuration
+
+Extend `config.yaml`:
+
+```yaml
+database:
+  enabled: true
+  path: "./data/newsletter-catalog.sqlite"
+```
+
+Behavior:
+
+- If `database.enabled` is omitted, it defaults to `true`.
+- Spreadsheet output remains controlled by the existing `output.excel.enabled` and `output.sheets_api.enabled` settings.
+- If all outputs are disabled, `nlc run` still writes to SQLite.
+
+## Web App
+
+Add `nlc serve [flags]`.
+
+Flags:
+
+- `--config PATH`, default `./config.yaml`
+- `--host HOST`, default `127.0.0.1`
+- `--port PORT`, default `3000`
+
+Views:
+
+- Dashboard: counts for newsletters, issues, links, sponsors, dead links, and recent runs.
+- Links: searchable table of content links with filters for newsletter, category, and date range.
+- Newsletter detail: issues and links for one newsletter.
+- Sponsored links: global sponsor table.
+- Dead links: global dead/unreachable table.
+- Runs: recent import run summaries.
+
+The first UI can use server-rendered HTML with minimal CSS. No SPA framework is required.
+
+## Data Flow
+
+Import:
+
+1. Gmail fetches configured label messages.
+2. Existing parser extracts links and sponsor entries.
+3. Existing cleanup/categorization/enrichment pipeline prepares rows.
+4. `DatabaseWriter` upserts newsletters, issues, links, occurrences, sponsors, dead links, and run summary.
+5. Optional spreadsheet writers run after database persistence when configured.
+
+Web:
+
+1. `nlc serve` opens the SQLite database.
+2. Request handlers query read-only catalog views.
+3. HTML pages render tables and simple filters.
+
+## Error Handling
+
+- Database open/migration errors are critical and stop `nlc run` or `nlc serve`.
+- A single failed row insert during import increments the run error count and stops the database transaction for that run.
+- SQLite writes use transactions so partial import data is not committed on failure.
+- Web route errors return a simple 500 page and log the error.
+
+## Testing
+
+Add tests for:
+
+- Config defaults for `database.enabled` and `database.path`.
+- Schema migration creates expected tables.
+- Database writer inserts newsletters, issues, links, sponsors, and dead links.
+- Duplicate normalized URLs are deduplicated while occurrences remain per issue.
+- `nlc run` writes to SQLite by default even when spreadsheet outputs are disabled.
+- Web routes render dashboard, links, sponsored links, dead links, and run history using a fixture database.
+- Existing spreadsheet writer tests continue to pass.
+
+## Out of Scope for This Pass
+
+- Browser-based Gmail OAuth setup.
+- Running Gmail imports from a web button.
+- User accounts or remote hosting.
+- Full visual design polish.
+- Migrating old JSON state into SQLite.
+- Removing Excel or Google Sheets support.
+
+## Acceptance Criteria
+
+- `nlc run` creates/updates the SQLite database by default.
+- `nlc serve` starts a local web app and displays imported catalog data.
+- Spreadsheet output still works when enabled.
+- Existing CLI validations remain green.
+- Tests cover database persistence and web read paths without live Gmail or Google credentials.