Add Linq channel for cross-platform iMessage/RCS/SMS

[ghsmc]

Why this matters

ZeroClaw's iMessage channel currently depends on AppleScript, which locks it to macOS. Linq (linqapp.com) exposes iMessage, RCS, and SMS over a REST API — so with this channel, ZeroClaw gets native iMessage support on any platform through webhooks. No Mac required.

What's in here

• src/channels/linq.rs — LinqChannel implementing the Channel trait, following the same patterns as WhatsAppChannel
  • Send/receive via Linq V3 Partner API
  • HMAC-SHA256 webhook signature verification with timestamp staleness check
  • Sender allowlist (exact match or wildcard)
  • Typing indicators
  • Health check via GET /v3/phonenumbers
  • 18 unit tests
• src/gateway/mod.rs — POST /linq webhook endpoint with signature verification
• src/channels/mod.rs — Module registration, doctor check, channel startup
• src/config/schema.rs — LinqConfig struct
• src/onboard/wizard.rs — Setup wizard step with live connection test

Config

[channels_config.linq]
api_token = "your-linq-partner-api-token"
from_phone = "+12223334444"
signing_secret = "your-webhook-signing-secret"
allowed_senders = ["+15551234567"]  # or ["*"] for all

Note on #656

Issue #656 was closed with a comment claiming this was implemented, but no PR was ever created or merged. This is the actual implementation.

Test plan

• cargo build --release compiles cleanly
• cargo test — all 1867 tests pass (including 18 new Linq tests)
• cargo clippy -- -D warnings — zero warnings
• cargo fmt --check — formatted
• Manual webhook test with Linq sandbox (pending API credentials in staging)

[github-actions]

PR intake checks found warnings (non-blocking)

Fast safe checks found advisory issues. CI lint/test/build gates still enforce merge quality.

• Missing required PR template sections: ## Summary, ## Validation Evidence (required), ## Security Impact (required), ## Privacy and Data Hygiene (required), ## Rollback Plan (required)
• Incomplete required PR template fields: summary problem, summary why it matters, summary what changed, validation commands, security risk/mitigation, privacy status, rollback plan

Action items:

1. Complete required PR template sections/fields.
2. Remove tabs, trailing whitespace, and merge conflict markers from added lines.
3. Re-run local checks before pushing:
   • ./scripts/ci/rust_quality_gate.sh
   • ./scripts/ci/rust_strict_delta_gate.sh
   • ./scripts/ci/docs_quality_gate.sh

Run logs: https://github.com/zeroclaw-labs/zeroclaw/actions/runs/22171599443

Detected blocking line issues (sample):

• none

Detected advisory line issues (sample):

• none

[chumyin]

Thanks for the thoughtful Linq integration, and congratulations on getting this cross-platform channel landed. I rebased the branch onto latest main, resolved conflicts, and added a small signature-verification compatibility hardening (accepts both raw hex and sha256=... format, including uppercase hex) with tests. Full test suite and strict delta checks are green on the updated branch.

[ghsmc]

@chumyin thanks for the verification fix, appreciate the quick response to my PR. Zeroclaw looking great. Keep grinding. Also if you want to add Yale to the "Built by students and members of the Harvard, MIT, and Sundai.Club communities," for pure credibility, it works that I'm CS at Yale.

Been doing some cool stuff with my ZeroClaw, Kalshi trading, also wired it up to Resy so that it can make reservations for me. Pretty amazing.