feat(agent): add human-like delay between block replies

Adds `agent.humanDelay` config option to create natural rhythm between
streamed message bubbles. When enabled, introduces a random delay
(default 800-2500ms) between block replies, making multi-message
responses feel more like natural human texting.

Config example:
```json
{
  "agent": {
    "blockStreamingDefault": "on",
    "humanDelay": {
      "enabled": true,
      "minMs": 800,
      "maxMs": 2500
    }
  }
}
```

- First message sends immediately
- Subsequent messages wait a random delay before sending
- Works with iMessage, Signal, and Discord providers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/concepts/messages.md

@@ -61,6 +61,7 @@ Key settings:
 - `agents.defaults.blockStreamingBreak` (`text_end|message_end`)
 - `agents.defaults.blockStreamingChunk` (`minChars|maxChars|breakPreference`)
 - `agents.defaults.blockStreamingCoalesce` (idle-based batching)
+- `agents.defaults.humanDelay` (human-like pause between block replies)
 - Provider overrides: `*.blockStreaming` and `*.blockStreamingCoalesce` (non-Telegram providers require explicit `*.blockStreaming: true`)
 
 Details: [Streaming + chunking](/concepts/streaming).

docs/concepts/streaming.md

@@ -71,6 +71,16 @@ progressive output.
 - Provider overrides are available via `*.blockStreamingCoalesce` (including per-account configs).
 - Default coalesce `minChars` is bumped to 1500 for Signal/Slack/Discord unless overridden.
 
+## Human-like pacing between blocks
+
+When block streaming is enabled, you can add a **randomized pause** between
+block replies (after the first block). This makes multi-bubble responses feel
+more natural.
+
+- Config: `agents.defaults.humanDelay` (override per agent via `agents.list[].humanDelay`).
+- Modes: `off` (default), `natural` (800–2500ms), `custom` (`minMs`/`maxMs`).
+- Applies only to **block replies**, not final replies or tool summaries.
+
 ## “Stream chunks or everything”
 
 This maps to: