#7459: fix(signal): resolve mention placeholders to actual names

## Summary Signal messages with @mentions contain placeholder characters (`\uFFFC`) in the message text, with actual name/number/uuid data in the `mentions` array. This patch processes the mentions array and replaces placeholders with readable `@name` text. ## Problem When someone sends a message like "Hey @Arthur check this" in Signal, OpenClaw receives: ```json { "message": "Hey \uFFFC check this", "mentions": [{"start": 4, "length": 1, "name": "Arthur", ...}] } ``` The agent sees garbled text instead of the actual mention. ## Solution Process the `mentions` array and replace placeholder characters with `@name` (falling back to number or uuid if name isn't available). Key points: - Sort mentions by position descending to replace from end first (preserves indices) - Use `name ?? number ?? uuid ?? "someone"` fallback chain - Minimal change, single file ## Testing - Tested locally with Signal group messages containing @mentions - Names now appear correctly as `@Arthur` instead of placeholder chars Fixes #7457 <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This change updates Signal inbound message parsing to render `@mentions` correctly by replacing the U+FFFC placeholder(s) in `dataMessage.message` using entries from `dataMessage.mentions`, sorting mentions from the end of the string to preserve indices. This improves the text that gets passed into the normal inbound envelope/session/dispatch flow (control command detection, debouncing, and agent routing) without changing downstream message handling. <h3>Confidence Score: 4/5</h3> - This PR is likely safe to merge and improves Signal message readability, with a small risk around malformed mention indices. - The change is localized to Signal inbound message text normalization and preserves existing flow (debouncing, command gating, dispatch). The main concern is robustness: defaulting missing `start/length` to `0/1` can produce incorrect replacements if mention metadata is absent/invalid, which would be user-visible but not catastrophic. - src/signal/monitor/event-handler.ts <!-- greptile_other_comments_section --> _{(3/5) Reply to the agent's comments like "Can you suggest a fix for this @greptileai?" or ask follow-up questions!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->