feat(desktop): promote Devin to a first-class managed ACP runtime

[errfld]

Tracked by #6. Blocked by #1.

Why this issue exists

Devin currently exists only in PRESET_HARNESSES as devin acp. That provides catalog/PATH discovery and generic spawning, but not the install, authentication, readiness, or model metadata projected from KnownAcpRuntime for Claude Code and Codex.

This promotes the existing identity; it does not add a second adapter or relay API.

Current code

• Preset: desktop/src-tauri/src/managed_agents/discovery/presets.rs
• Tier-1 table and Desktop arg normalization: desktop/src-tauri/src/managed_agents/discovery.rs
• Metadata type: desktop/src-tauri/src/managed_agents/discovery/runtime_metadata.rs
• Standalone arg normalization: crates/buzz-acp/src/config.rs
• Readiness: desktop/src-tauri/src/managed_agents/readiness.rs and readiness/cli_login.rs
• Discovery/install: desktop/src-tauri/src/commands/agent_discovery.rs
• ACP auth: desktop/src-tauri/src/commands/agent_auth.rs
• Reserved IDs: desktop/src-tauri/src/managed_agents/custom_harnesses.rs

Target contract

Use #1 as authority. Expected metadata unless disproved:

Field	Value
id / label	devin / Devin
command / args	devin / ["acp"]
underlying CLI	devin; native ACP, no adapter
auth probe / login	devin auth status / devin auth login
model env	DEVIN_MODEL
provider env	none; Devin-owned account/provider
config path	~/.config/devin/config.json
MCP sidecar	none initially
skill directory	none; Devin reads .agents/skills
thinking/context/token env	none unless official docs establish one

Use current official platform install metadata. Devin is proprietary and externally installed; do not vendor its binary or credentials.

Implementation guidance

1. Move Devin from PRESET_HARNESSES into KNOWN_ACP_RUNTIMES, preserving its ID.
2. Keep launch args declarative. Prefer adding default_args to KnownAcpRuntime and consuming it in Desktop discovery/spawn instead of creating another command table. The independent buzz-acp CLI still needs equivalent standalone normalization.
3. Generalize collect_missing_requirements so known runtimes with auth_probe_args use cli_login::requirements; retain specialized Buzz Agent/Goose checks.
4. Ensure discovery returns one built-in Devin entry populated by the existing parallel auth-probe phase.
5. Verify generic auth discovery/connect works once known_acp_runtime_exact("devin") resolves; add no Devin auth match arm.
6. Derive reserved IDs from runtime/preset sources of truth.
7. Reuse the bundled logo from Add Devin as a preset ACP harness block/buzz#3225; add no remote icon.
8. Reconcile fix(acp): launch ACP/stdio mode for managed agents with no runtime preset block/buzz#3804: promoted Devin args must come from the known-runtime path while its generic preset fallback remains for other presets.

Acceptance criteria

• Existing records/personas with runtime: "devin" work without migration.
• Devin appears exactly once with source: "builtin".
• Missing CLI, logged-out, invalid-config, and ready states are distinct and actionable.
• Managed, persona-linked, and command-override launches execute devin acp.
• buzz-acp helper commands normalize bare devin to devin acp.
• Browser/terminal login methods come from ACP initialize.authMethods.
• Credentials and credential files are never read, copied, persisted, or logged.
• Official install metadata and all paths above have focused tests.
• Claude, Codex, Goose, Buzz Agent, presets, and custom harnesses are unchanged.

Tests to update

• desktop/src-tauri/src/managed_agents/discovery/tests.rs
• readiness tests beside managed_agents/readiness.rs
• desktop/src-tauri/src/commands/agent_auth.rs fake-executable tests
• desktop/src-tauri/src/commands/agent_discovery.rs install-plan tests
• desktop/src-tauri/src/managed_agents/runtime/tests.rs
• desktop/src-tauri/src/managed_agents/custom_harnesses.rs collision tests
• crates/buzz-acp/src/config.rs arg-normalization tests
• replace existing Devin preset tests while preserving the logo guard

Suggested verification

. ./bin/activate-hermit
cargo test -p buzz-acp
cargo test --manifest-path desktop/src-tauri/Cargo.toml managed_agents::
cargo test --manifest-path desktop/src-tauri/Cargo.toml commands::agent_auth
just fmt-check
just desktop-tauri-fmt-check

Run just ci before review and commit with git commit -s.

Out of scope

• Onboarding/config UI (feat(desktop): add Devin onboarding, models, and config integration #3)
• Real lifecycle proof/docs (test(docs): verify and document the managed Devin lifecycle #4)
• Permission brokerage (feat(acp): route permission requests to authorized Buzz owners #5)
• Editing or reading Devin credentials
• Cloud Devin, Outposts, or remote Devin MCP

References

• Add Devin as a preset ACP harness block/buzz#3225
• feat(acp): bring your own harness (BYOH) — generic ACP runtime seam + settings gallery block/buzz#2773
• fix(acp): launch ACP/stdio mode for managed agents with no runtime preset block/buzz#3804
• https://docs.devin.ai/cli
• https://cdn.agentclientprotocol.com/registry/v1/latest/registry.json