feat: write leafs incrementally without rebuilding the graph. (#29)

Ladybug 0.19 stays FTS/HNSW queryable on MERGE of new ids; DROP INDEX
was the fatal path. bin/brain/add.go and POST /ingest land facts+info
in one transaction so watch/mail/git can become leafs now (Gitea #14).

docs/design.md

@@ -80,14 +80,16 @@ Conflicting pairings (≥2 yes vs ≥2 no) = hypothesis (OQ1 → v2 resolution).
 They do not exec Python. Control questions for recall@5 live in
 `internal/brain/rank` so CI can test the table without libladybug.
 Python `bin/kb/{get,stats,eval}` remain for GitHub Actions until the runner
-fetches Zig + libs (`bin/cgo/zig`). Index/write is still `bin/kb/index`
+fetches Zig + libs (`bin/cgo/zig`). Incremental write is `bin/kb/add`
+(`bin/brain/add.go`). Bulk index/write is still `bin/kb/index`
 (`docker compose --profile index`).
 
 ## Agent API (D20)
 
 `bin/brain/serve.go` exposes the same `internal/httpapi.Ops` table as OpenAPI
 (`GET /openapi.json`) and MCP (`POST /mcp` JSON-RPC `tools/list` +
-`tools/call`). Tool names match paths: `search`, `get`, `stats`, `audit`.
+`tools/call`). Tool names match paths: `search`, `get`, `stats`, `audit`,
+`ingest` (add a leaf; omit body for the CLI hint).
 Agents should use these endpoints instead of shebang CLIs.
 
 ## Reasoner (D18)
@@ -98,5 +100,5 @@ CPU sidecar: compose profile `reasoner` (`OLLAMA_NUM_GPU=0`,
 `127.0.0.1:11435`). Bake-off: `bin/reasoner/bakeoff.go`. Weights stay out
 of the 2dph image. See [docs/reasoner.md](reasoner.md).
 
-Gap to v1 (write, hops, corpus, agent loop): [roadmap](roadmap.md),
+Gap to v1 (hops, corpus, CI eval): [roadmap](roadmap.md),
 [epic #16](https://git.produktor.io/eSlider/2dph/issues/16).

docs/roadmap.md

@@ -23,8 +23,9 @@ Decisions: [PLAN.md](../PLAN.md).
 Read path Go + Zig CGO (D21). HTTP + OpenAPI + MCP (D20). PicoClaw compose
 profile + CPU reasoner (D18). Mail sync → import → rebuild. D14 shebangs.
 Compose `api` (no CPython) / `index` (Python write). Issues #1–#5, #7–#13.
-
-`POST /ingest` is a rebuild **hint**. `add` is not implemented.
+[#15](https://git.produktor.io/eSlider/2dph/issues/15) lever/loop.
+[#14](https://git.produktor.io/eSlider/2dph/issues/14) `bin/brain/add.go` /
+`POST /ingest` (Python `kblib.add_leafs`; no Go upsert port).
 
 ## Blockers
 
@@ -34,24 +35,18 @@ question
     ├─ FTS + HNSW          ← in
     ├─ facts / info roots  ← in
     ├─ web (D17)           ← in
+    ├─ brain/add ACID      ← in
     ├─ Cypher hop          ← #17  schema yes, search no
-    ├─ brain/add ACID      ← #14  rebuild only
     └─ facts+chats corpus  ← #18
 ```
 
-1. **[#14](https://git.produktor.io/eSlider/2dph/issues/14) write** —
-   `bin/brain/index.go --rebuild` (Python `kblib`). No incremental
-   `brain/add`. Watch/mail/git cannot become facts “now”.
-2. **[#17](https://git.produktor.io/eSlider/2dph/issues/17) hops** —
+1. **[#17](https://git.produktor.io/eSlider/2dph/issues/17) hops** —
    `Leaf-[:FROM_FILE]->File-[:HAS_VERSION]->Commit-[:AUTHORED]->Person`
    exists; `--hop` still errors. Without a walk, D9/D10 are paper.
-3. **[#18](https://git.produktor.io/eSlider/2dph/issues/18) corpus** —
+2. **[#18](https://git.produktor.io/eSlider/2dph/issues/18) corpus** —
    rebuild loads repo markdown + mail as `info`. `facts/extract` pairing
    and `bin/chats` are not indexed. WhatsApp is a stub. PII stays in `var/`.
-4. **[#15](https://git.produktor.io/eSlider/2dph/issues/15) lever/loop** —
-   2dph is the lever (`search` → `get` → `audit`). PicoClaw is the loop.
-   Document the contour in-repo; CPU turns need a large context window.
-5. **[#19](https://git.produktor.io/eSlider/2dph/issues/19) CI eval** —
+3. **[#19](https://git.produktor.io/eSlider/2dph/issues/19) CI eval** —
    recall SoT should be `bin/brain/eval.go` via Zig, not Python `bin/kb/eval`.
 
 ## Not v1
@@ -61,7 +56,6 @@ contradiction resolution, OQ3 duckdb-md export, OQ4 YAML-first leafs.
 
 ## Close epic #16 when
 
-- facts+info can be written without a full rebuild for every leaf
 - `--hop` stops erroring and runs a Cypher path from search hits
 - ops pairing + chat import land as leafs on rebuild
 - MCP tool order is documented and still gated by tests

docs/runbook.md

@@ -43,10 +43,12 @@ That binds `127.0.0.1:8888`. JSON format must stay enabled.
 
 ## Index then search
 
-Write path is Compose profile `index` (Python Ladybug rebuild) until
-`brain/add` is v2. The operator command is `bin/brain/index.go`.
+Write path is `bin/brain/add.go` for a leaf (or `POST /ingest`). Bulk
+corpus rebuild remains `bin/brain/index.go --rebuild` (Compose profile
+`index`). Do not DROP INDEX on Ladybug 0.19.
 
 ```bash
+bin/brain/add.go --text "arc-1 runs Matrix" --root facts --source "compose.yml x docker ps"
 bin/brain/index.go --rebuild
 bin/brain/search.go "LadybugDB vector index"     # facts → info → web (D17)
 bin/brain/search.go "upstream flag" --no-web