diff --git a/AGENTS.md b/AGENTS.md
index 985370c..7f76d15 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -40,7 +40,7 @@ PLAN.md       decisions + execution + open questions
 docs/         published docs
 skills/       in-project agent skills (vendored, no external links)
 bin/          self-describing tools bin/{subject}/{method}.go (shebang)
-bin/brain/    search.go serve.go index.go get.go stats.go eval.go watch.go
+bin/brain/    search.go serve.go index.go add.go get.go stats.go eval.go watch.go
 bin/chats/    sync.go import.go facts.go apply.go; libs in internal/chats
 bin/mail/     sync.go import.go (index_mail → brain/index.go)
 bin/markdown/ import.go (H2 leaf split; Python bin/md/import fallback)
@@ -74,9 +74,9 @@ bin/brain/index.go --rebuild                                            # rebuil
   `pdftotext -layout` fast path (~15ms); textless/scanned PDFs fall back to
   docling (isolated subprocess — its native onnx can segfault the parent).
   Conversion never touches the brain DB (crash safety).
-- `index_mail` is a deprecation shim for `bin/brain/index.go --rebuild`. Ladybug
-  corrupts its WAL when brand-new leafs are bulk-inserted while FTS/vector
-  indexes exist; a fresh DB with indexes created last is the only safe path.
+- `index_mail` is a deprecation shim for `bin/brain/index.go --rebuild`. Bulk
+  rebuild still deletes `var/kb.lbug` and creates FTS/HNSW last. Single-leaf
+  write is `bin/brain/add.go` (safe while indexes exist; do not DROP INDEX).
   Keep conversion + indexing separate so a conversion crash can't leave the
   DB mid-transaction.
 
@@ -89,6 +89,8 @@ bin/kb/search "query" [--repo X]                  # deprecated wrapper → bin/b
 bin/brain/search.go "query" [--root facts|info]   # deduction search → YAML
 bin/brain/search.go "query" --no-web              # local graph only
 eval "$(bin/cgo/zig env)"                         # Zig cc + liblbug (not gcc)
+bin/brain/add.go --text T --root facts --source "a.md x b.md"  # incremental write
+bin/brain/add.go --json                                      # stdin leaf or {leafs:[...]}
 bin/brain/get.go <id> [--body] [--json]          # Go read; Python bin/kb/get CI fallback
 bin/brain/stats.go [--json]
 bin/brain/eval.go [--json]                       # recall@5; questions in internal/brain/rank
diff --git a/PLAN.md b/PLAN.md
index cb6e5e6..0b867ac 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -31,9 +31,9 @@ detective method: **a fact needs ≥2 independent sources or it is
 | D3 | web search | Go client `bin/web/search.go` (`internal/websearch`). SearXNG URL is config (`BRAIN_SEARCH_URL`). Optional Compose profile `searxng` (sanitized settings). Do not run a second copy on a host that already has one. Empty/`throttled` ≠ “nothing exists”. |
 | D4 | embeddings | **model2vec** `minishlab/potion-multilingual-128M` instead of embeddinggemma. |
 | D5 | parser | **mistune** for MD → leaf extraction (duckdb-md documented as future optional SQL/export layer, not v1). |
-| D6 | graph engine | **LadybugDB**. Go is the service (`bin/brain/search.go`, `bin/brain/serve.go` in-process, `internal/brain`). Read path is Go + Zig CGO (D21). Python `bin/kb/{get,stats,eval}` is the CI fallback when Zig/libs are not fetched. Index/write stays Python (`compose --profile index`) until the Go write path is safe. |
+| D6 | graph engine | **LadybugDB**. Go is the service (`bin/brain/search.go`, `bin/brain/serve.go` in-process, `internal/brain`). Read path is Go + Zig CGO (D21). Python `bin/kb/{get,stats,eval}` is the CI fallback when Zig/libs are not fetched. Incremental write is Python `bin/kb/add` (`bin/brain/add.go`). Bulk rebuild stays `compose --profile index` until the Go write path is safe. |
 | D7 | db access | `db-yaml`/`psql-yq`-style, read-only, YAML out. OnlyOffice Postgres via SSH tunnel (`127.0.0.1:5433`). |
-| D8 | evidence | detective method: ≥2 independent sources or `(not confirmed)`. Auto-pair docker ps × compose × ssh-config × docs. |
+| D8 | evidence | detective method: ≥2 independent sources or `(not confirmed)`. 2-source auto-pair docker ps × compose × ssh-config × docs. |
 | D9 | facts/goal model | Who / What / How / Where / When + evidence + confidence on every edge. |
 | D10 | versioning | everything is a leaf with `sha256 + observed_at + source_rev`; `File-[:HAS_VERSION]->Commit-[:AUTHORED]->Person`. Stale = `source_rev` < git HEAD. |
 | D11 | strong/weak | `root` column: `facts` (strong) vs `info` (weak). Answer is `confirmed` only from facts root. |
@@ -45,7 +45,7 @@ detective method: **a fact needs ≥2 independent sources or it is
 | D17 | assertion gate | Fact-check every *claim* (facts → info → live → web), not every edit. `bin/brain/search.go` adds a `web` block when there is no facts hit (`throttled`/`skipped`/`refused` ≠ absence). `--root` and `--no-web` stay local. Missing graph ≠ “does not exist”. |
 | D18 | reasoner | Pluggable OpenAI-compatible URL (`REASONER_BASE_URL`). RAM: `Qwen/Qwen3.5-9B`. Quality: `prism-ml/Bonsai-27B-gguf` or `Qwen/Qwen3.6-27B`. No official Qwen3.6-9B. CPU bake-off: `bin/reasoner/bakeoff.go` + compose profile `reasoner` (`OLLAMA_NUM_GPU=0`, `:11435`). PicoClaw is compose profile `picoclaw`; tools are `search`/`get`/`audit`. Weights are not copied into the 2dph image. Agent lever/loop: [#15](https://git.produktor.io/eSlider/2dph/issues/15). |
 | D19 | git history | [go-git](https://github.com/go-git/go-git) via `bin/git/import.go`. No subprocess of the git binary. Conversion prints commit leafs; brain write is `bin/brain/index.go`. |
-| D20 | agent API | OpenAPI + MCP are generated from the same `internal/httpapi.Ops` table as `bin/brain/serve.go` handlers. `GET /openapi.json`, `POST /mcp` (JSON-RPC tools/list + tools/call). Tool names match OpenAPI paths (`search`/`get`/`stats`/`audit`). |
+| D20 | agent API | OpenAPI + MCP are generated from the same `internal/httpapi.Ops` table as `bin/brain/serve.go` handlers. `GET /openapi.json`, `POST /mcp` (JSON-RPC tools/list + tools/call). Tool names match OpenAPI paths (`search`/`get`/`stats`/`audit`/`ingest`). |
 | D21 | CGO | Ladybug/tokenizers CGO is compiled with **Zig** (`bin/cgo/zcc` → `zig cc -target …-linux-gnu`), not gcc. `bin/cgo/zig` pins Zig 0.14.1 + liblbug 0.19.1 + libtokenizers 1.27.0. Compose `target: api` has no CPython; write/rebuild is profile `index`. |
 
 ## Architecture
@@ -57,8 +57,10 @@ detective method: **a fact needs ≥2 independent sources or it is
   skills/                   in-project skills (web-search, postgres, brain, picoclaw, diataxis-docs)
   bin/
     facts/extract.go audit.go crm.go  # D14 shebang; Python implementation
-    kb/index                Python write path (called by bin/brain/index.go)
+    kb/index                Python bulk write (called by bin/brain/index.go)
+    kb/add                  Python incremental write (called by bin/brain/add.go)
     brain/index.go          rebuild FTS + HNSW (incl. --with-mail)
+    brain/add.go            incremental leaf write (no rebuild)
     brain/get.go stats.go eval.go  # Go read (cgo); Python bin/kb/* CI fallback
     brain/watch.go
     brain/search.go         deduction: facts → info → web-search
@@ -160,18 +162,19 @@ Feedback loop: every commit → PR → CI → green/gate → merge. Same discipl
 
 ## Gap to v1 (epic #16)
 
-Read path + MCP are in. The detective brain is not closed until the graph is
-**writable incrementally** and search can **walk** it. Board:
+Read path + MCP are in. Incremental `brain/add` is in. The detective brain is
+not closed until search can **walk** the graph and the facts+chats corpus
+lands on rebuild. Board:
 [epic #16](https://git.produktor.io/eSlider/2dph/issues/16),
 milestone [v1 detective brain](https://git.produktor.io/eSlider/2dph/milestone/12).
 Narrative: [docs/roadmap.md](docs/roadmap.md).
 
 | Order | Issue | Gap |
 |-------|-------|-----|
-| 1 | [#14](https://git.produktor.io/eSlider/2dph/issues/14) | Write stays Python rebuild; `brain/add` / `POST /ingest` are hints. Ladybug 0.19 WAL corrupts if new leafs land while FTS/HNSW exist. |
+| 1 | [#14](https://git.produktor.io/eSlider/2dph/issues/14) | **in** — `bin/brain/add.go` / `POST /ingest` write facts+info without deleting `kb.lbug`. Bulk corpus still `--rebuild`. Leftover Python (mail/facts) is not the living-graph blocker. |
 | 2 | [#17](https://git.produktor.io/eSlider/2dph/issues/17) | `--hop` errors. `FROM_FILE` / `HAS_VERSION` are in schema; search does not walk them. |
 | 3 | [#18](https://git.produktor.io/eSlider/2dph/issues/18) | Rebuild is mostly `info` (repo md + mail). `facts/extract` and chats are not a first-class index input. WhatsApp sync is a stub. |
-| 4 | [#15](https://git.produktor.io/eSlider/2dph/issues/15) | Lever = 2dph fact-check. Loop = PicoClaw/MCP `search` → `get` → `audit`. Specify in-repo, not only live config. |
+| 4 | [#15](https://git.produktor.io/eSlider/2dph/issues/15) | **in** — lever/loop documented (`search` → `get` → `audit`). |
 | 5 | [#19](https://git.produktor.io/eSlider/2dph/issues/19) | GitHub CI recall still runs Python `bin/kb/eval`. |
 
 Does **not** block epic close: [#6](https://git.produktor.io/eSlider/2dph/issues/6) OCR, OQ1, OQ3, OQ4.
\ No newline at end of file
diff --git a/README.md b/README.md
index 20a72ea..659ae98 100644
--- a/README.md
+++ b/README.md
@@ -120,6 +120,7 @@ Mail is a first-class corpus (retrievable through the same search):
 ```bash
 bin/mail/sync.go --source onlyoffice,gmail --workers 8 --out var/mail  # raw sync (Go)
 bin/mail/import.go --from-raw var/mail                                  # JSON → markdown
+bin/brain/add.go --text T --root facts --source "a.md x b.md"
 bin/brain/index.go --rebuild                                            # rebuild brain (incl. mail)
 bin/brain/search.go "invoice from last week"                            # same search over mail leafs
 ```
@@ -128,8 +129,9 @@ bin/brain/search.go "invoice from last week"                            # same s
 
 - **LadybugDB** — single `var/kb.lbug`, Cypher + HNSW + BM25, embedded.
   Read tools (`get` / `stats` / `eval`) are Go + Zig CGO (`bin/cgo/zcc`).
-  Python fallbacks stay for CI until the runner fetches Zig. Write is
-  Compose profile `index` (`bin/brain/index.go`).
+  Python fallbacks stay for CI until the runner fetches Zig. Incremental
+  write is `bin/brain/add.go` (Python `kblib.add_leafs`). Bulk rebuild is
+  Compose profile `index` (`bin/brain/index.go --rebuild`).
 - **model2vec** — `potion-multilingual-128M` (256-dim), CPU, no Ollama
   runtime dependency.
 - facts and info split by `root` but written in the same transaction.
diff --git a/bin/brain/add.go b/bin/brain/add.go
new file mode 100755
index 0000000..23e817f
--- /dev/null
+++ b/bin/brain/add.go
@@ -0,0 +1,21 @@
+//usr/bin/env go run -tags=brain_add "$0" "$@"; exit
+//go:build brain_add
+//
+// bin/brain/add.go - incremental leaf write (Python kblib, no rebuild).
+//
+//	./bin/brain/add.go --text T --root facts --source "a.md x b.md"
+//	./bin/brain/add.go --json
+//
+// D6: write stays Python. Does not delete var/kb.lbug.
+// NOTE: never run `gofmt -w` on this file — it breaks the shebang.
+package main
+
+import (
+	"os"
+
+	"github.com/eSlider/2dph/internal/cmdbin"
+)
+
+func main() {
+	os.Exit(cmdbin.ExecFile("bin/kb/add", os.Args[1:]))
+}
diff --git a/bin/brain/index.go b/bin/brain/index.go
index d58e2f4..d896632 100755
--- a/bin/brain/index.go
+++ b/bin/brain/index.go
@@ -7,8 +7,8 @@
 //	./bin/brain/index.go --rebuild --with-mail
 //	./bin/brain/index.go --dry-run --with-mail
 //
-// v1 write is always a rebuild when mail is included (live FTS/HNSW + bulk
-// insert corrupts Ladybug 0.19 WAL). `add` is v2.
+// v1 write: bin/brain/add.go for one/few leafs (indexes may already exist).
+// Bulk mail/corpus still --rebuild (fresh file, indexes last).
 // NOTE: never run `gofmt -w` on this file — it breaks the shebang.
 package main
 
diff --git a/bin/kb/add b/bin/kb/add
new file mode 100755
index 0000000..14aa0d8
--- /dev/null
+++ b/bin/kb/add
@@ -0,0 +1,114 @@
+#!/usr/bin/env python3
+"""kb/add - incremental leaf write (no rebuild).
+
+  bin/kb/add --text T --root facts|info --source S
+  bin/kb/add --json                 # stdin: one object or {"leafs":[...]}
+  bin/kb/add --db PATH --json
+
+Writes facts+info in one Ladybug transaction. Does not delete kb.lbug.
+Embedding is used when provided; otherwise model2vec encodes the text.
+"""
+from __future__ import annotations
+
+import json
+import sys
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[2]
+sys.path.insert(0, str(ROOT / "bin" / "tools"))
+
+from kblib import (  # noqa: E402
+    EMBED_DIM,
+    add_leafs,
+    connect,
+    ensure_indexes,
+    init_schema,
+)
+
+
+def _as_leafs(payload: object) -> list[dict]:
+    if isinstance(payload, list):
+        return [dict(x) for x in payload]
+    if isinstance(payload, dict):
+        if "leafs" in payload:
+            return [dict(x) for x in payload["leafs"]]
+        return [dict(payload)]
+    raise ValueError("json must be an object, a list, or {leafs:[...]}")
+
+
+def _embed_missing(leafs: list[dict]) -> None:
+    missing = [lf for lf in leafs if not lf.get("embedding")]
+    if not missing:
+        return
+    from model2vec import StaticModel
+
+    model = StaticModel.from_pretrained("minishlab/potion-multilingual-128M")
+    for lf in missing:
+        text = str(lf.get("text") or "")
+        vec = model.encode([text])[0].astype(float).tolist()
+        if len(vec) != EMBED_DIM:
+            vec = (vec + [0.0] * EMBED_DIM)[:EMBED_DIM]
+        lf["embedding"] = vec
+
+
+def main(argv: list[str]) -> int:
+    import argparse
+
+    p = argparse.ArgumentParser(description="add leafs without rebuilding the brain")
+    p.add_argument("--db", default="", help="path to kb.lbug (default var/kb.lbug)")
+    p.add_argument("--json", action="store_true", help="read leaf JSON from stdin")
+    p.add_argument("--text", default="", help="leaf text")
+    p.add_argument("--root", default="info", choices=("facts", "info"))
+    p.add_argument("--source", default="")
+    p.add_argument("--confidence", default="confirmed")
+    p.add_argument("--source-rev", default="working-tree")
+    p.add_argument("--how", default="brain/add")
+    p.add_argument("--loc", default="")
+    p.add_argument("--type", default="reference", dest="type_")
+    args = p.parse_args(argv)
+
+    if args.json:
+        raw = sys.stdin.read()
+        if not raw.strip():
+            print("kb/add: empty stdin", file=sys.stderr)
+            return 2
+        leafs = _as_leafs(json.loads(raw))
+    else:
+        if not args.text or not args.source:
+            print("kb/add: --text and --source are required (or --json)", file=sys.stderr)
+            return 2
+        leafs = [{
+            "text": args.text,
+            "root": args.root,
+            "source": args.source,
+            "confidence": args.confidence,
+            "source_rev": args.source_rev,
+            "how": args.how,
+            "loc": args.loc or args.source,
+            "type": args.type_,
+        }]
+
+    for lf in leafs:
+        if not lf.get("text") or not lf.get("source"):
+            print("kb/add: each leaf needs text and source", file=sys.stderr)
+            return 2
+
+    _embed_missing(leafs)
+
+    from kblib import DB_PATH, VAR
+
+    dbpath = Path(args.db) if args.db else DB_PATH
+    dbpath.parent.mkdir(parents=True, exist_ok=True)
+    VAR.mkdir(exist_ok=True)
+    db, conn = connect(dbpath, read_only=False)
+    init_schema(conn)
+    ids = add_leafs(conn, leafs)
+    ensure_indexes(conn)
+    conn.close()
+    db.close()
+    print(json.dumps({"mode": "add", "ids": ids, "db": str(dbpath)}))
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))
diff --git a/bin/tools/kblib.py b/bin/tools/kblib.py
index 028ebc1..5841739 100644
--- a/bin/tools/kblib.py
+++ b/bin/tools/kblib.py
@@ -4,7 +4,7 @@ Single embedded graph `var/kb.lbug`. Two roots: facts (assertions backed by
 >=2 independent sources) and info (narrative leafs). Hybrid retrieval: BM25
 (FTS extension) + HNSW cosine (VECTOR extension) + Cypher graph hops.
 
-All access is read-only unless `--rebuild` is passed to kb/index.
+All access is read-only unless `--rebuild` (kb/index) or `kb/add`.
 """
 from __future__ import annotations
 
@@ -118,6 +118,50 @@ def upsert_leaf(conn: ladybug.Connection, *, text: str, root: str, confidence: s
     return lid
 
 
+def add_leafs(conn: ladybug.Connection, leafs: list[dict]) -> list[str]:
+    """Write facts+info leafs in one transaction. Safe while FTS/HNSW exist.
+
+    Each leaf dict: text, source, optional root/confidence/source_rev/how/loc/type/embedding.
+    Does not delete the database file. Measured on Ladybug 0.19: MERGE of new
+    ids (and updates) stays FTS+HNSW queryable; DROP INDEX is the fatal path.
+    """
+    if not leafs:
+        return []
+    started = False
+    try:
+        conn.execute("BEGIN TRANSACTION")
+        started = True
+    except Exception:
+        started = False
+    ids: list[str] = []
+    try:
+        for lf in leafs:
+            ids.append(
+                upsert_leaf(
+                    conn,
+                    text=str(lf["text"]),
+                    root=str(lf.get("root") or ROOT_INFO),
+                    confidence=str(lf.get("confidence") or CONF_CONFIRMED),
+                    source=str(lf["source"]),
+                    source_rev=str(lf.get("source_rev") or "working-tree"),
+                    how=str(lf.get("how") or "brain/add"),
+                    loc=str(lf.get("loc") or lf.get("source") or ""),
+                    type_=str(lf.get("type") or lf.get("type_") or "reference"),
+                    embedding=lf.get("embedding"),
+                )
+            )
+        if started:
+            conn.execute("COMMIT")
+    except Exception:
+        if started:
+            try:
+                conn.execute("ROLLBACK")
+            except Exception:
+                pass
+        raise
+    return ids
+
+
 def leaf_index_names(conn: ladybug.Connection) -> set[str]:
     """Return index names on the Leaf table (e.g. {'id', 'Leaf_vec', '_PK'})."""
     rows = conn.execute("CALL SHOW_INDEXES() RETURN *").get_all()
diff --git a/bin/tools/test_bin_layout.py b/bin/tools/test_bin_layout.py
index b1f50b4..88691b0 100644
--- a/bin/tools/test_bin_layout.py
+++ b/bin/tools/test_bin_layout.py
@@ -75,9 +75,20 @@ class BinLayoutTest(unittest.TestCase):
         )
 
     def test_brain_methods_are_shebangs(self) -> None:
-        for method in ("index.go", "get.go", "stats.go", "eval.go", "watch.go"):
+        for method in ("index.go", "add.go", "get.go", "stats.go", "eval.go", "watch.go"):
             self._assert_shebang(f"bin/brain/{method}")
 
+    def test_brain_add_is_python_write_not_rebuild(self) -> None:
+        self._assert_shebang("bin/brain/add.go")
+        text = (ROOT / "bin" / "brain" / "add.go").read_text()
+        self.assertIn("cmdbin.ExecFile", text)
+        self.assertIn("bin/kb/add", text)
+        self.assertNotIn("--rebuild", text)
+        py = (ROOT / "bin" / "kb" / "add").read_text()
+        self.assertIn("add_leafs", py)
+        self.assertIn("--json", py)
+        self.assertNotIn("unlink", py.lower())
+
     def test_brain_get_stats_eval_are_not_python_exec(self) -> None:
         for method in ("get.go", "stats.go", "eval.go"):
             text = (ROOT / "bin" / "brain" / method).read_text()
diff --git a/bin/tools/test_kb_add.py b/bin/tools/test_kb_add.py
new file mode 100644
index 0000000..2e32276
--- /dev/null
+++ b/bin/tools/test_kb_add.py
@@ -0,0 +1,69 @@
+"""Incremental add writes leafs without deleting kb.lbug."""
+from __future__ import annotations
+
+import json
+import os
+import subprocess
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[2]
+
+
+class KbAddCLITest(unittest.TestCase):
+    def test_json_add_does_not_delete_db(self) -> None:
+        tmp = Path(tempfile.mkdtemp())
+        dbpath = tmp / "kb.lbug"
+        py = sys.executable
+        venv_py = ROOT / ".venv" / "bin" / "python"
+        if venv_py.is_file():
+            py = str(venv_py)
+        payload = {
+            "text": "cli zebra leaf",
+            "root": "info",
+            "source": "cli-test",
+            "confidence": "confirmed",
+            "how": "test",
+            "loc": str(tmp),
+            "type": "reference",
+            "embedding": [0.0] * 256,
+        }
+        payload["embedding"][0] = 0.3
+        proc = subprocess.run(
+            [py, str(ROOT / "bin" / "kb" / "add"), "--db", str(dbpath), "--json"],
+            cwd=ROOT,
+            input=json.dumps(payload),
+            capture_output=True,
+            text=True,
+            env=os.environ.copy(),
+            check=False,
+        )
+        self.assertEqual(proc.returncode, 0, proc.stderr)
+        self.assertTrue(dbpath.exists(), "add must create the db, not skip write")
+        out = json.loads(proc.stdout)
+        self.assertEqual(out.get("mode"), "add")
+        self.assertEqual(len(out.get("ids") or []), 1)
+        again = subprocess.run(
+            [py, str(ROOT / "bin" / "kb" / "add"), "--db", str(dbpath), "--json"],
+            cwd=ROOT,
+            input=json.dumps({
+                **payload,
+                "text": "second moose leaf",
+                "source": "cli-test-2",
+            }),
+            capture_output=True,
+            text=True,
+            env=os.environ.copy(),
+            check=False,
+        )
+        self.assertEqual(again.returncode, 0, again.stderr)
+        self.assertTrue(dbpath.exists())
+        second = json.loads(again.stdout)
+        self.assertEqual(len(second.get("ids") or []), 1)
+        self.assertNotEqual(out["ids"][0], second["ids"][0])
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/bin/tools/test_kblib.py b/bin/tools/test_kblib.py
index 7e5e28c..b9e1c60 100644
--- a/bin/tools/test_kblib.py
+++ b/bin/tools/test_kblib.py
@@ -71,6 +71,69 @@ class KblibTest(unittest.TestCase):
         self.assertTrue(hits)
         self.assertIn("Leaf_vec", kblib.leaf_index_names(self.conn))
 
+    def test_add_after_indexes_keeps_fts_queryable(self):
+        """Incremental add after FTS+HNSW must find the new leaf on both indexes."""
+        kblib.upsert_leaf(self.conn, text="seed fox leaf", root="info",
+                          confidence="confirmed", source="s", source_rev="r1",
+                          how="test", loc="/tmp", type_="reference",
+                          embedding=make_emb(0.1))
+        kblib.ensure_indexes(self.conn)
+        ids = kblib.add_leafs(self.conn, [{
+            "text": "added zebra after index",
+            "root": "facts",
+            "confidence": "confirmed",
+            "source": "a.md x b.md",
+            "source_rev": "r1",
+            "how": "test",
+            "loc": "/tmp",
+            "type": "fact",
+            "embedding": make_emb(0.9),
+        }])
+        self.assertEqual(len(ids), 1)
+        fts = kblib.query_fts(self.conn, "zebra", 5)
+        self.assertTrue(fts)
+        self.assertIn("zebra", fts[0]["text"])
+        self.assertEqual(fts[0]["root"], "facts")
+        vec = kblib.query_vector(self.conn, make_emb(0.9), 5)
+        self.assertTrue(any("zebra" in h["text"] for h in vec))
+        fox = kblib.query_fts(self.conn, "fox", 5)
+        self.assertTrue(fox)
+        self.assertIn("fox", fox[0]["text"])
+
+    def test_add_facts_and_info_one_transaction(self):
+        """D12: facts and info land in the same transaction."""
+        kblib.ensure_indexes(self.conn)
+        ids = kblib.add_leafs(self.conn, [
+            {
+                "text": "tx fact leaf two-source",
+                "root": "facts",
+                "confidence": "confirmed",
+                "source": "compose.yml x docker ps",
+                "source_rev": "r1",
+                "how": "test",
+                "loc": "/tmp",
+                "type": "fact",
+                "embedding": make_emb(0.4),
+            },
+            {
+                "text": "tx info narrative",
+                "root": "info",
+                "confidence": "confirmed",
+                "source": "note.md",
+                "source_rev": "r1",
+                "how": "test",
+                "loc": "/tmp",
+                "type": "reference",
+                "embedding": make_emb(0.5),
+            },
+        ])
+        self.assertEqual(len(ids), 2)
+        stats = kblib.stats(self.conn)
+        self.assertEqual(stats["by_root"].get("facts"), 1)
+        self.assertEqual(stats["by_root"].get("info"), 1)
+        self.assertTrue(kblib.query_fts(self.conn, "two-source", 5))
+        self.assertTrue(kblib.query_fts(self.conn, "narrative", 5))
+
     def test_drop_vector_then_create_raises_clear_error(self):
         """DROP INDEX leaves ghost catalog; create_fts_and_vector must raise."""
         kblib.upsert_leaf(self.conn, text="seed", root="info",
diff --git a/docs/design.md b/docs/design.md
index c16b85d..96b51f1 100644
--- a/docs/design.md
+++ b/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).
\ No newline at end of file
diff --git a/docs/roadmap.md b/docs/roadmap.md
index 6e0552d..623549c 100644
--- a/docs/roadmap.md
+++ b/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
diff --git a/docs/runbook.md b/docs/runbook.md
index 3f1087e..ff34c4a 100644
--- a/docs/runbook.md
+++ b/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
diff --git a/internal/brain/http.go b/internal/brain/http.go
index c65a5dc..1bd5311 100644
--- a/internal/brain/http.go
+++ b/internal/brain/http.go
@@ -7,6 +7,8 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"os/exec"
+	"path/filepath"
 
 	"github.com/eSlider/2dph/internal/brain/rank"
 )
@@ -137,12 +139,22 @@ func (HTTP) Audit(context.Context) ([]byte, error) {
 	return json.Marshal(map[string]any{"status": "ok", "by_confidence": rows})
 }
 
-func (HTTP) Ingest(context.Context) ([]byte, error) {
-	return json.Marshal(map[string]any{
-		"mode":    "rebuild",
-		"command": "bin/brain/index.go --rebuild",
-		"add":     "v2",
-	})
+func (HTTP) Ingest(ctx context.Context, body []byte) ([]byte, error) {
+	if len(bytes.TrimSpace(body)) == 0 {
+		return json.Marshal(map[string]any{
+			"mode":    "add",
+			"command": "bin/brain/add.go",
+			"rebuild": "bin/brain/index.go --rebuild",
+		})
+	}
+	cmd := exec.CommandContext(ctx, filepath.Join(repoRoot(), "bin", "kb", "add"), "--json")
+	cmd.Stdin = bytes.NewReader(body)
+	cmd.Dir = repoRoot()
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, fmt.Errorf("add: %w", err)
+	}
+	return out, nil
 }
 
 func asInt(v any) int64 {
diff --git a/internal/httpapi/mcp.go b/internal/httpapi/mcp.go
index dbd6d16..3f39668 100644
--- a/internal/httpapi/mcp.go
+++ b/internal/httpapi/mcp.go
@@ -144,7 +144,15 @@ func (s *Server) mcpCall(r *http.Request, params json.RawMessage) (any, error) {
 			return nil, fmt.Errorf("cancelled")
 		}
 		defer s.release()
-		body, err = s.api.Ingest(r.Context())
+		var payload []byte
+		text := strings.TrimSpace(fmt.Sprint(p.Arguments["text"]))
+		if text != "" && text != "<nil>" {
+			payload, err = json.Marshal(p.Arguments)
+			if err != nil {
+				return nil, err
+			}
+		}
+		body, err = s.api.Ingest(r.Context(), payload)
 	default:
 		return nil, fmt.Errorf("unknown tool %s", p.Name)
 	}
diff --git a/internal/httpapi/server.go b/internal/httpapi/server.go
index 061dce5..8dea1c3 100644
--- a/internal/httpapi/server.go
+++ b/internal/httpapi/server.go
@@ -11,6 +11,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"io"
 	"log"
 	"net/http"
 	"os"
@@ -27,7 +28,7 @@ type API interface {
 	Get(ctx context.Context, id string, body bool) ([]byte, error)
 	Stats(ctx context.Context) ([]byte, error)
 	Audit(ctx context.Context) ([]byte, error)
-	Ingest(ctx context.Context) ([]byte, error)
+	Ingest(ctx context.Context, body []byte) ([]byte, error)
 }
 
 type Server struct {
@@ -59,7 +60,7 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	case PathAudit:
 		s.handleJSON(w, r, s.api.Audit)
 	case PathIngest:
-		s.handleJSON(w, r, s.api.Ingest)
+		s.handleIngest(w, r)
 	case PathOpenAPI:
 		s.handleOpenAPI(w, r)
 	case PathMCP:
@@ -116,6 +117,24 @@ func (s *Server) handleJSON(w http.ResponseWriter, r *http.Request, fn func(cont
 	writeAPI(w, body, err)
 }
 
+func (s *Server) handleIngest(w http.ResponseWriter, r *http.Request) {
+	var raw []byte
+	if r.Method == http.MethodPost {
+		b, err := io.ReadAll(io.LimitReader(r.Body, 1<<20))
+		if err != nil {
+			writeJSON(w, http.StatusBadRequest, map[string]any{"error": "read body"})
+			return
+		}
+		raw = b
+	}
+	if !s.acquire(w, r) {
+		return
+	}
+	defer s.release()
+	body, err := s.api.Ingest(r.Context(), raw)
+	writeAPI(w, body, err)
+}
+
 func (s *Server) tryAcquire(r *http.Request) bool {
 	return s.acquire(nopWriter{}, r)
 }
@@ -191,11 +210,30 @@ func (ExecSearcher) Get(context.Context, string, bool) ([]byte, error) {
 }
 func (ExecSearcher) Stats(context.Context) ([]byte, error) { return nil, errUnimplemented }
 func (ExecSearcher) Audit(context.Context) ([]byte, error) { return nil, errUnimplemented }
-func (ExecSearcher) Ingest(context.Context) ([]byte, error) {
-	return json.Marshal(map[string]any{
-		"mode":    "rebuild",
-		"command": "bin/brain/index.go --rebuild",
-	})
+func (b ExecSearcher) Ingest(ctx context.Context, body []byte) ([]byte, error) {
+	if len(strings.TrimSpace(string(body))) == 0 {
+		return json.Marshal(map[string]any{
+			"mode":    "add",
+			"command": "bin/brain/add.go",
+			"rebuild": "bin/brain/index.go --rebuild",
+		})
+	}
+	root := os.Getenv("KB_ROOT")
+	if root == "" {
+		root = "."
+	}
+	cmd := exec.CommandContext(ctx, filepath.Join(root, "bin/kb/add"), "--json")
+	cmd.Stdin = strings.NewReader(string(body))
+	cmd.Dir = root
+	out, err := cmd.Output()
+	if err != nil {
+		var exitErr *exec.ExitError
+		if errors.As(err, &exitErr) {
+			return nil, errors.New("add failed: " + strings.TrimSpace(string(exitErr.Stderr)))
+		}
+		return nil, err
+	}
+	return out, nil
 }
 
 func defaultSearchCmd(root string) string {
diff --git a/internal/httpapi/server_test.go b/internal/httpapi/server_test.go
index 2ea3462..01d8482 100644
--- a/internal/httpapi/server_test.go
+++ b/internal/httpapi/server_test.go
@@ -1,6 +1,7 @@
 package httpapi
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"net/http"
@@ -64,8 +65,11 @@ func (f *fakeSearcher) Audit(context.Context) ([]byte, error) {
 	return []byte(`{"status":"ok"}`), nil
 }
 
-func (f *fakeSearcher) Ingest(context.Context) ([]byte, error) {
-	return []byte(`{"mode":"rebuild","command":"bin/brain/index.go --rebuild"}`), nil
+func (f *fakeSearcher) Ingest(_ context.Context, body []byte) ([]byte, error) {
+	if len(bytes.TrimSpace(body)) == 0 {
+		return []byte(`{"mode":"add","command":"bin/brain/add.go"}`), nil
+	}
+	return []byte(`{"mode":"add","ids":["fake-leaf"]}`), nil
 }
 
 func (f *fakeSearcher) count() int {
@@ -193,6 +197,27 @@ func TestStatsAuditIngest(t *testing.T) {
 	}
 }
 
+func TestIngestIsAddNotRebuildHint(t *testing.T) {
+	h := NewServer(&fakeSearcher{}, 1)
+	code, body := get(t, h, "/ingest")
+	if code != http.StatusOK {
+		t.Fatalf("GET /ingest code = %d body=%s", code, body)
+	}
+	if strings.Contains(string(body), `"add":"v2"`) || strings.Contains(string(body), "write is v2") {
+		t.Fatalf("GET /ingest still a v2 hint: %s", body)
+	}
+	if !strings.Contains(string(body), "bin/brain/add.go") {
+		t.Fatalf("GET /ingest should name add.go: %s", body)
+	}
+	code, body = postJSON(t, h, "/ingest", `{"text":"hello","root":"info","source":"t"}`)
+	if code != http.StatusOK {
+		t.Fatalf("POST /ingest code = %d body=%s", code, body)
+	}
+	if !strings.Contains(string(body), "fake-leaf") {
+		t.Fatalf("POST /ingest should add: %s", body)
+	}
+}
+
 func TestHTTPPackageDoesNotExecPython(t *testing.T) {
 	raw, err := os.ReadFile("server.go")
 	if err != nil {
diff --git a/internal/httpapi/spec.go b/internal/httpapi/spec.go
index 37d4a7d..f20bdff 100644
--- a/internal/httpapi/spec.go
+++ b/internal/httpapi/spec.go
@@ -47,7 +47,15 @@ var Ops = []Op{
 	},
 	{Path: PathStats, Method: "get", ID: "stats", Summary: "index health", MCP: true},
 	{Path: PathAudit, Method: "get", ID: "audit", Summary: "facts confidence histogram", MCP: true},
-	{Path: PathIngest, Method: "get", ID: "ingest", Summary: "rebuild hint (write is v2)", MCP: true},
+	{
+		Path: PathIngest, Method: "post", ID: "ingest", Summary: "add a leaf without rebuild",
+		MCP: true,
+		Params: []Param{
+			{Name: "text", In: "query", Type: "string", Description: "leaf text (omit for CLI hint)"},
+			{Name: "root", In: "query", Type: "string", Description: "facts or info (default info)"},
+			{Name: "source", In: "query", Type: "string", Description: "evidence pointer; facts need two sources"},
+		},
+	},
 	{Path: PathOpenAPI, Method: "get", ID: "openapi", Summary: "OpenAPI 3 document for this server"},
 }
 
diff --git a/internal/httpapi/spec_test.go b/internal/httpapi/spec_test.go
index 07286db..1884245 100644
--- a/internal/httpapi/spec_test.go
+++ b/internal/httpapi/spec_test.go
@@ -38,11 +38,24 @@ func TestMCPToolsMatchOpenAPIPaths(t *testing.T) {
 			t.Fatalf("MCP tool %s has no OpenAPI path %s", tool.Name, path)
 		}
 	}
-	for _, need := range []string{"search", "get", "stats", "audit"} {
+	for _, need := range []string{"search", "get", "stats", "audit", "ingest"} {
 		if !names[need] {
 			t.Fatalf("MCP tools missing %s: %v", need, names)
 		}
 	}
+	var ingest MCPTool
+	for _, tool := range tools {
+		if tool.Name == "ingest" {
+			ingest = tool
+			break
+		}
+	}
+	if strings.Contains(ingest.Description, "v2") {
+		t.Fatalf("ingest still a v2 hint: %s", ingest.Description)
+	}
+	if !strings.Contains(ingest.Description, "add") {
+		t.Fatalf("ingest should describe add: %s", ingest.Description)
+	}
 }
 
 func TestOpenAPIHTTP(t *testing.T) {
diff --git a/skills/brain/SKILL.md b/skills/brain/SKILL.md
index 261cd05..f15eac8 100644
--- a/skills/brain/SKILL.md
+++ b/skills/brain/SKILL.md
@@ -26,6 +26,7 @@ second independent source when local roots cannot confirm. An answer is
 bin/brain/search.go "Matrix federation"                # pointers + snippets, YAML
 bin/brain/search.go "onlyoffice postgres" --root facts # restrict to confirmed
 bin/brain/search.go "where is cs-lexicon" --json | yq '.[].ref'
+bin/brain/add.go --text T --root facts --source "a.md x b.md"
 bin/brain/get.go <id> --body                           # full chunk only when needed
 bin/brain/stats.go                                     # index health
 bin/brain/eval.go                                      # recall@5 >= 0.95 gate (Go; Python bin/kb/eval is CI fallback)
diff --git a/skills/brain/tools.md b/skills/brain/tools.md
index fd66429..033cd3e 100644
--- a/skills/brain/tools.md
+++ b/skills/brain/tools.md
@@ -8,4 +8,4 @@ Serve: `bin/brain/serve.go` (`GET /openapi.json`, `POST /mcp`).
 - `get` — read one leaf by id
 - `stats` — index health
 - `audit` — facts confidence histogram
-- `ingest` — rebuild hint (write is v2)
+- `ingest` — add a leaf without rebuild