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+# Pivot Forecast — CLAUDE.md
+
+## What this app is
+
+A web app for building named forecast scenarios against any PostgreSQL table. The workflow: load historical actuals as a baseline (optionally date-shifted into the forecast period), then apply incremental adjustments (scale, recode, clone) to build a plan. All changes are append-only, fully audited, and reversible by log entry.
+
+Full spec: `pf_spec.md`
+Data transport architecture options: `pf_perspective_options.md`
+UX mockup: `pf_ux_mockup.md`
+Open work: `todo.md`
+
+---
+
+## Tech stack
+
+- **Backend:** Node.js / Express (`server.js`), runs on port 3010
+- **Database:** PostgreSQL — isolated `pf` schema
+- **Frontend:** React + Vite + Tailwind CSS in `ui/`; built output lands in `public/app/`
+- **Pivot:** [Perspective](https://perspective.finos.org/) 4.4.0 loaded from CDN at runtime
+- **Dev:** `npm run dev` (nodemon) in root; `npm run build` in `ui/`
+
+---
+
+## Project layout
+
+```
+server.js               Express entry point; pg pool; type parsers for bigint/numeric
+routes/
+  tables.js             GET /api/tables, /api/tables/:schema/:tname/preview
+  sources.js            Source registration, col_meta, SQL generation
+  versions.js           Version CRUD, baseline/reference load, data stream
+  operations.js         scale, recode, clone, undo — the core forecast ops
+  log.js                GET /api/versions/:id/log, DELETE /api/log/:logid
+lib/
+  sql_generator.js      buildFilterClause, token substitution helpers
+  utils.js
+setup_sql/
+  01_schema.sql         pf schema DDL — run once to install
+ui/src/
+  views/
+    Setup.jsx           DB browser, source registration, col_meta editor
+    Baseline.jsx        Version management, baseline workbench, reference load
+    Forecast.jsx        Perspective pivot + operation panel (Scale/Recode/Clone)
+    Sidebar.jsx         3-step collapsible nav
+    StatusBar.jsx       Source · version · row count · status
+    Timeline.jsx        Date-range preview bar for baseline segments
+```
+
+---
+
+## Database schema (`pf`)
+
+- **`pf.source`** — registered source tables
+- **`pf.col_meta`** — column roles: `dimension` | `value` | `units` | `date` | `filter` | `ignore`; `is_key` marks dimensions used in slice WHERE clauses
+- **`pf.version`** — named forecast scenarios; `exclude_iters` (default `["reference"]`) blocks those iter values from all operations
+- **`pf.fc_{tname}_{version_id}`** — one forecast table per version; contains both operational rows (`iter = baseline|scale|recode|clone`) and reference rows (`iter = reference`)
+- **`pf.log`** — audit log; every write gets one entry; `slice` + `params` stored as jsonb
+- **`pf.sql`** — generated SQL templates per source/operation; tokens substituted at request time
+
+### Key token substitution tokens
+`{{fc_table}}`, `{{where_clause}}`, `{{exclude_clause}}`, `{{logid}}`, `{{pf_user}}`, `{{value_incr}}`, `{{units_incr}}`, `{{pct}}`, `{{set_clause}}`, `{{scale_factor}}`, `{{date_offset}}`, `{{filter_clause}}`
+
+---
+
+## Core data flow
+
+### Initial load (Forecast view)
+`GET /api/versions/:id/data` → Arrow IPC binary stream → `worker.table(buffer)` in Perspective WASM
+
+**Why one batch (not streaming):** pg returns `bigint`/`numeric` as strings by default — type parsers in `server.js` coerce them to numbers. Per-batch Arrow encoding creates independent dictionaries that cause Perspective WASM to crash on dictionary replacement messages. Server accumulates all rows, emits one record batch.
+
+### Forecast operations
+POST to `/api/versions/:id/{scale|recode|clone}` → SQL executed with `RETURNING *` → new rows returned as JSON → `pspTable.update(rows)` — no full reload.
+
+### Undo
+`DELETE /api/log/:logid` → removes rows by logid → **full Perspective reload** (known wart).
+
+---
+
+## Slice mechanics
+
+When the user clicks a pivot cell, `perspective-click` fires. The handler in `Forecast.jsx` extracts `[col, '==', value]` filters from `detail.config.filter` — only `role = dimension` columns are kept as the slice. This slice populates the operation panel and is sent as the `slice` object in all operation POST bodies.
+
+**Limitation:** computed columns created by Perspective's split_by (e.g. Month, YearDate) don't map back to raw rows — only native dimension columns work for slice extraction.
+
+---
+
+## Operation SQL patterns
+
+All three operations follow the same structure: insert a `pf.log` row in a CTE, then insert forecast rows referencing its id. `{{where_clause}}` is built from the slice; `{{exclude_clause}}` blocks `exclude_iters` rows.
+
+- **Scale** — distributes `value_incr`/`units_incr` proportionally across rows in the slice using window functions
+- **Recode** — inserts negative rows (zero out original) + positive rows with `{{set_clause}}` dimension overrides; both share the same logid
+- **Clone** — copies the slice with `{{set_clause}}` overrides and `{{scale_factor}}` multiplier; original untouched
+
+`build_where()` validates every slice key against col_meta (only `role = dimension` allowed). Values are escaped but not parameterized — consistent with existing patterns, debuggable in pg logs.
+
+---
+
+## Known issues / active work (see todo.md for detail)
+
+- Operation panel (Scale/Recode/Clone) wiring to API is a stub — needs completion
+- Status bar is hardcoded — needs to reflect actual selected source/version
+- Load progress bar is jittery — needs throttle (~10 updates/sec)
+- Default pivot layout should be configurable per source (currently hardcodes first 2 dimensions)
+- Source/version selection doesn't persist across page reload
+- Col_meta / version schema drift: if col_meta roles change after a version's forecast table is created, SQL and DDL go out of sync — workaround is to delete and recreate the version
+
+## Deferred (not in v1)
+Baseline replay (`replay: true` returns 501), approval workflow, territory filtering, export, version comparison, multi-DB connections.
diff --git a/package.json b/package.json
index 7e028cb..e4583d9 100644
--- a/package.json
+++ b/package.json
@@ -3,6 +3,7 @@
   "version": "1.0.0",
   "description": "Pivot Forecast Application",
   "main": "server.js",
+  "license": "MIT",
   "scripts": {
     "start": "node server.js",
     "dev": "nodemon server.js",