#12064: fix: prevent chunker from truncating messages that fit within limit

## Bug The message chunker introduced in 191da1feb unpredictably truncates messages mid-sentence on Signal, TUI, and other channels — even when the text fits within the channel's textChunkLimit. ## Root Cause `sendTextChunks()` in `deliver.ts` always passes text through the chunker pipeline regardless of whether splitting is needed. The chunker can return partial/empty results for text that doesn't need chunking. ## Fix 1. **Skip chunking when text fits:** If `text.length <= textLimit`, send directly without invoking the chunker. 2. **Guard empty chunker output:** If chunker returns an empty array, send the original text intact instead of silently dropping it. ## Reproduction Send any multi-paragraph message via Signal or TUI on v2026.2.6-3. Messages are randomly cut mid-sentence. ## Workaround Add `"chunker": null` to each channel in openclaw.json. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> Change is localized to `src/infra/outbound/deliver.ts` and adjusts outbound text delivery to avoid invoking the channel chunker when the text already fits within `textChunkLimit`, and to fall back to sending the original text if the chunker returns an empty array. This targets a regression where some chunkers could return partial/empty output and truncate messages even when no splitting was required. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk once the small cleanup is addressed. - The change is narrow and preserves existing behavior except for skipping chunking when unnecessary and guarding empty chunker output. No new external dependencies or complex logic were introduced; the only actionable issue found is an unresolved placeholder reference in a new comment. - src/infra/outbound/deliver.ts (comment cleanup) <!-- greptile_other_comments_section --> <!-- /greptile_comment -->