feat(skill): add channel-formatting skill (#1448)

feat(skill): channel-aware text formatting for WhatsApp, Telegram, Slack, Signal

.claude/skills/channel-formatting/SKILL.md

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+---
+name: channel-formatting
+description: Convert Claude's Markdown output to each channel's native text syntax before delivery. Adds zero-dependency formatting for WhatsApp, Telegram, and Slack (marker substitution). Also ships a Signal rich-text helper (parseSignalStyles) used by the Signal skill.
+---
+
+# Channel Formatting
+
+This skill wires channel-aware Markdown conversion into the outbound pipeline so Claude's
+responses render natively on each platform — no more literal `**asterisks**` in WhatsApp or
+Telegram.
+
+| Channel | Transformation |
+|---------|---------------|
+| WhatsApp | `**bold**` → `*bold*`, `*italic*` → `_italic_`, headings → bold, links flattened |
+| Telegram | same as WhatsApp |
+| Slack | same as WhatsApp, but links become `<url\|text>` |
+| Discord | passthrough (Discord already renders Markdown) |
+| Signal | passthrough for `parseTextStyles`; `parseSignalStyles` in `src/text-styles.ts` produces plain text + native `textStyle` ranges for use by the Signal skill |
+
+Code blocks (fenced and inline) are always protected — their content is never transformed.
+
+## Phase 1: Pre-flight
+
+### Check if already applied
+
+```bash
+test -f src/text-styles.ts && echo "already applied" || echo "not yet applied"
+```
+
+If `already applied`, skip to Phase 3 (Verify).
+
+## Phase 2: Apply Code Changes
+
+### Ensure the upstream remote
+
+```bash
+git remote -v
+```
+
+If an `upstream` remote pointing to `https://github.com/qwibitai/nanoclaw.git` is missing,
+add it:
+
+```bash
+git remote add upstream https://github.com/qwibitai/nanoclaw.git
+```
+
+### Merge the skill branch
+
+```bash
+git fetch upstream skill/channel-formatting
+git merge upstream/skill/channel-formatting
+```
+
+If there are merge conflicts on `package-lock.json`, resolve them by accepting the incoming
+version and continuing:
+
+```bash
+git checkout --theirs package-lock.json
+git add package-lock.json
+git merge --continue
+```
+
+For any other conflict, read the conflicted file and reconcile both sides manually.
+
+This merge adds:
+
+- `src/text-styles.ts` — `parseTextStyles(text, channel)` for marker substitution and
+  `parseSignalStyles(text)` for Signal native rich text
+- `src/router.ts` — `formatOutbound` gains an optional `channel` parameter; when provided
+  it calls `parseTextStyles` after stripping `<internal>` tags
+- `src/index.ts` — both outbound `sendMessage` paths pass `channel.name` to `formatOutbound`
+- `src/formatting.test.ts` — test coverage for both functions across all channels
+
+### Validate
+
+```bash
+npm install
+npm run build
+npx vitest run src/formatting.test.ts
+```
+
+All 73 tests should pass and the build should be clean before continuing.
+
+## Phase 3: Verify
+
+### Rebuild and restart
+
+```bash
+npm run build
+launchctl kickstart -k gui/$(id -u)/com.nanoclaw   # macOS
+# Linux: systemctl --user restart nanoclaw
+```
+
+### Spot-check formatting
+
+Send a message through any registered WhatsApp or Telegram chat that will trigger a
+response from Claude. Ask something that will produce formatted output, such as:
+
+> Summarise the three main advantages of TypeScript using bullet points and **bold** headings.
+
+Confirm that the response arrives with native bold (`*text*`) rather than raw double
+asterisks.
+
+### Check logs if needed
+
+```bash
+tail -f logs/nanoclaw.log
+```
+
+## Signal Skill Integration
+
+If you have the Signal skill installed, `src/channels/signal.ts` can import
+`parseSignalStyles` from the newly present `src/text-styles.ts`:
+
+```typescript
+import { parseSignalStyles, SignalTextStyle } from '../text-styles.js';
+```
+
+`parseSignalStyles` returns `{ text: string, textStyle: SignalTextStyle[] }` where
+`textStyle` is an array of `{ style, start, length }` objects suitable for the
+`signal-cli` JSON-RPC `textStyles` parameter (format: `"start:length:STYLE"`).
+
+## Removal
+
+```bash
+# Remove the new file
+rm src/text-styles.ts
+
+# Revert router.ts to remove the channel param
+git diff upstream/main src/router.ts   # review changes
+git checkout upstream/main -- src/router.ts
+
+# Revert the index.ts sendMessage call sites to plain formatOutbound(rawText)
+# (edit manually or: git checkout upstream/main -- src/index.ts)
+
+npm run build
+```