fix: bind remote Claude agents to native CLI

[troyhoffman-oss]

Summary

• bind remote Claude ACP adapters to the host native Claude Code launcher instead of the adapter SDK bundle
• reserve CLAUDE_CODE_EXECUTABLE against persona/user overrides
• support both Claude ACP adapter names and document/preflight the vendor CLI requirement

Verification

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test -p buzz-backend-ssh (107 passed)
• desktop TypeScript tests (3,843 passed) and production build
• desktop Tauri check and full tests (1,803 passed, 14 ignored; diagnostics 3 passed)
• web production build
• Flutter tests (695 passed, 1 skipped)
• sh -n, dash -n, ShellCheck, git diff --check
• GitHub: unit tests, all four desktop smoke shards, both Linux cross-compiles, relay E2E, backend integration, and both desktop integration shards passed

Existing branch-wide and infrastructure gate failures

The remaining red checks are unrelated to this five-file change:

• desktop file-size gate: unchanged desktop/src-tauri/src/events.rs is 1,011 lines against a 1,000-line limit
• buzz-db: unchanged nanosecond timestamp precision assertion in replica_fence::tests::fence_starts_closed_and_opens_on_advance
• Rust lint: unchanged desktop/src-tauri/src/huddle/pipeline.rs fails the desktop Tauri rustfmt check
• dependency policy: existing yanked spin 0.9.8/0.10.0 lockfile entries
• macOS desktop build: unchanged mesh-llm dependency checkout is missing after cargo fetch
• Windows Rust: clippy exposes seven pre-existing Unix-only test helpers as dead code; every reported definition and use predates this commit
• Docker matrix: all four images build, then GHCR rejects cache-layer export with permission_denied for the GitHub installation

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Apply the native Claude binding to remote model probes

When the create dialog selects a remote Claude harness, discover.rs::models_script still invokes buzz-acp models --json without resolving or exporting CLAUDE_CODE_EXECUTABLE. Consequently, model discovery continues to use the adapter's bundled Claude binary while the deployed service uses the native launcher resolved here, so the catalog/authentication check can describe a different Claude installation than the one that actually handles turns. Reuse this resolution and binding in the remote probe path as well.

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