docs: document streaming + chunking

docs/concepts/agent.md

@@ -102,6 +102,7 @@ Control soft block chunking with `agent.blockStreamingChunk` (defaults to
 800–1200 chars; prefers paragraph breaks, then newlines; sentences last).
 Verbose tool summaries are emitted at tool start (no debounce); Control UI
 streams tool output via agent events when available.
+More details: [Streaming + chunking](/concepts/streaming).
 
 ## Configuration (minimal)
 

docs/concepts/streaming.md

@@ -0,0 +1,85 @@
+---
+summary: "Streaming + chunking behavior (block replies, draft streaming, limits)"
+read_when:
+  - Explaining how streaming or chunking works on providers
+  - Changing block streaming or provider chunking behavior
+  - Debugging duplicate/early block replies or draft streaming
+---
+# Streaming + chunking
+
+Clawdbot has two separate “streaming” layers:
+- **Block streaming (providers):** emit completed **blocks** as the assistant writes. These are normal provider messages (not token deltas).
+- **Token-ish streaming (Telegram only):** update a **draft bubble** with partial text while generating; final message is sent at the end.
+
+There is **no real token streaming** to external provider messages today. Telegram draft streaming is the only partial-stream surface.
+
+## Block streaming (provider messages)
+
+Block streaming sends assistant output in coarse chunks as it becomes available.
+
+```
+Model output
+  └─ text_delta/events
+       ├─ (blockStreamingBreak=text_end)
+       │    └─ chunker emits blocks as buffer grows
+       └─ (blockStreamingBreak=message_end)
+            └─ chunker flushes at message_end
+                   └─ provider send (block replies)
+```
+Legend:
+- `text_delta/events`: model stream events (may be sparse for non-streaming models).
+- `chunker`: `EmbeddedBlockChunker` applying min/max bounds + break preference.
+- `provider send`: actual outbound messages (block replies).
+
+**Controls:**
+- `agent.blockStreamingDefault`: `"on"`/`"off"` (default on).
+- `agent.blockStreamingBreak`: `"text_end"` or `"message_end"`.
+- `agent.blockStreamingChunk`: `{ minChars, maxChars, breakPreference? }`.
+- Provider hard cap: `*.textChunkLimit` (e.g., `whatsapp.textChunkLimit`).
+
+**Boundary semantics:**
+- `text_end`: stream blocks as soon as chunker emits; flush on each `text_end`.
+- `message_end`: wait until assistant message finishes, then flush buffered output.
+
+`message_end` still uses the chunker if the buffered text exceeds `maxChars`, so it can emit multiple chunks at the end.
+
+## Chunking algorithm (low/high bounds)
+
+Block chunking is implemented by `EmbeddedBlockChunker`:
+- **Low bound:** don’t emit until buffer >= `minChars` (unless forced).
+- **High bound:** prefer splits before `maxChars`; if forced, split at `maxChars`.
+- **Break preference:** `paragraph` → `newline` → `sentence` → `whitespace` → hard break.
+- **Code fences:** never split inside fences; when forced at `maxChars`, close + reopen the fence to keep Markdown valid.
+
+`maxChars` is clamped to the provider `textChunkLimit`, so you can’t exceed per-provider caps.
+
+## “Stream chunks or everything”
+
+This maps to:
+- **Stream chunks:** `blockStreamingDefault: "on"` + `blockStreamingBreak: "text_end"` (emit as you go).
+- **Stream everything at end:** `blockStreamingBreak: "message_end"` (flush once, possibly multiple chunks if very long).
+- **No block streaming:** `blockStreamingDefault: "off"` (only final reply).
+
+## Telegram draft streaming (token-ish)
+
+Telegram is the only provider with draft streaming:
+- Uses Bot API `sendMessageDraft` in **private chats with topics**.
+- `telegram.streamMode: "partial" | "block" | "off"`.
+  - `partial`: draft updates with the latest stream text.
+  - `block`: draft updates in chunked blocks (same chunker rules).
+  - `off`: no draft streaming.
+- Final reply is still a normal message.
+- `/reasoning stream` writes reasoning into the draft bubble (Telegram only).
+
+When draft streaming is active, Clawdbot disables block streaming for that reply to avoid double-streaming.
+
+```
+Telegram (private + topics)
+  └─ sendMessageDraft (draft bubble)
+       ├─ streamMode=partial → update latest text
+       └─ streamMode=block   → chunker updates draft
+  └─ final reply → normal message
+```
+Legend:
+- `sendMessageDraft`: Telegram draft bubble (not a real message).
+- `final reply`: normal Telegram message send.