Host support: Devin CLI — native plugin manifest, portable compatibility, and versioned MCP/hook profiles

[ScriptedAlchemy]

Scope / evidence

P2 feature expansion with availability gating. Research date 2026-09-06; Agent Bundle baseline 5fc8de37c9695b816d55bdcf18a6bcb1dfee69f5. Official docs read, no Devin CLI installation or authenticated run. The current plugin guide labels the feature closed beta. Do not advertise generally available support until tested with an eligible host/account/version.

This issue primarily targets local Devin CLI. Cloud Devin and Devin Desktop have related but different capabilities; do not claim cloud parity from a local test or confuse the Devin MCP service with the CLI's MCP-client configuration.

Primary specifications

• CLI overview and supported installation platforms
• Plugin manifests, compatible layouts, dependency policy and management
• Skill authoring format
• Lifecycle hook inputs and outputs
• MCP configuration and versioned config-file migration
• Full official documentation index

Verified integration model

Devin's native root marker is .devin-plugin/plugin.json, with shared skills, optional AGENTS.md, triggered rules, custom agents, root hooks.json, and .mcp.json. The documented compatibility order is native Devin manifest, Claude manifest, then root Agent Plugins manifest. Therefore merely adding portable plugin.json to an existing Claude composite does not ensure Devin will use portable semantics.

The native manifest supports explicit skill paths and MCP declarations. Empty skill lists and empty MCP declarations have different convention-suppression behavior; do not apply a generic empty-means-disabled rule. Required/optional/forbidden plugin lists are host policy, not ordinary npm dependencies.

Proposed native fixture

composite-root/
  .devin-plugin/plugin.json
  AGENTS.md
  skills/review/SKILL.md
  hooks.json
  config/devin-mcp.json
  mcp/example.mjs

{
  "name": "example-plugin",
  "version": "1.0.0",
  "skills": ["skills"],
  "mcpServers": { "paths": ["config/devin-mcp.json"], "exclusive": true }
}

This is an illustrative emitted manifest, not a request for authors to duplicate their application declarations. The exclusive MCP binding is useful only when accepted by the pinned native parser; test that it really suppresses a foreign .mcp.json.

Operator workflow

devin plugins install ./composite-root
devin plugins install example/repository
devin plugins list
devin plugins info example-plugin
devin plugins update example-plugin
devin plugins remove example-plugin

Local plugin installations are linked references with changes visible on a subsequent session. Keep the reference at a stable owned location; do not leave a native registration pointing to a deleted temporary epoch. Preserve native installation confirmation and governance lists. Do not automatically use --yes, install optional dependencies, or delete required plugins that the host intentionally retains after removing the parent.

MCP configuration differences

The official reference documents a change beginning with v3000.3: MCP moves from main config files to dedicated mcp_config.json files. Project/local/user locations differ; current local overrides use .devin/mcp_config.local.json. Reuse the actual host CLI instead of hardcoding an old config location:

devin mcp add -s project example -- node /absolute/composite-root/mcp/example.mjs
devin mcp list
devin mcp get example

Example dedicated configuration:

{"mcpServers":{"example":{"command":"node","args":["/absolute/composite-root/mcp/example.mjs"]}}}

Do not register that independent definition if the plugin already supplies the same server. Keep secrets in native operator configuration/OAuth; plugin-supplied confidential OAuth secrets are not permitted by the plugin contract. Native versus portable root/data interpolation and data deletion on uninstall must be tested, not copied from another host.

Hooks and runtime mapping

Use event-specific native payload codecs. Session and per-turn identifiers are distinct. Before-tool hooks can modify input or express a decision; prompt/stop events have their own output shapes. Current plugin documentation explicitly describes hooks as best-effort/fail-open: do not sell them as a security boundary or guarantee blocking when loading fails.

Reuse canonical preflight/operation execution only for supported semantics. A typed operation exposed by MCP does not require a native subagent or hook. Local custom agents and prompt hooks must not be projected into cloud sessions where unsupported. Avoid arbitrary Python/shell authoring solely to match documentation examples; generate the needed native envelope around existing compiled JS.

Composite, packaging and acceptance

• Pin eligible CLI version/account prerequisite and native/Claude/portable manifest precedence.
• Test a skills-only package with no synthetic MCP/Flight/state runtime.
• Verify configured skill paths, empty-list behavior, triggered rules and namespace collisions through native discovery.
• Test explicit MCP source precedence and suppression with existing Claude/portable documents present.
• Run an actual generated tool from a relocated read-only artifact without source, preserving input/schema/outcome/argv/env.
• Exercise hook execute/deny/continue, context mutation, failure and timeout; accurately describe fail-open limitations.
• Test local linked install, update, disabled/policy-blocked state, removal, and required-plugin retention.
• Verify package code versus native plugin data ownership, including native uninstall semantics; no unowned-directory deletion.
• Record native success separately from parser checks or a beta-access refusal.
• Add Composite conformance: test cross-host auto-discovery and precedence, not only file collisions #651 effective-discovery and Small-plugin acceptance: skills and plain hooks without an unnecessary MCP/RSC runtime or empty Workbench #652 small-plugin acceptance; do not disable AB4106 globally.

Non-goals

No cloud orchestration, automatic beta enrollment, organization governance changes, shared credential storage, new dependency manager, second compiler, or guarantee that all Devin surfaces have the same feature set.

[ScriptedAlchemy]

Resolved by #721 (72a8857ebe).

Devin CLI — observed Agent Plugins 1.0.0; docs retrieved 2026-09-06, plugins documented as closed beta. Supported: the emitted package installs as one plugin.

Surface	State	Evidence
manifest	supported	2026-09-06: https://docs.devin.ai/cli/extensibility/plugins/overview states "plugins packaged per the open Agent Plugins 1.0.0 spec (a plugin.json manifest at the plugin root, MCP servers in a root mcp.json, skills under skills/) load too", and that "an unrecognized $schema version is warned about and the plugin still loads best-effort".
skills	supported	2026-09-06: https://docs.devin.ai/cli/extensibility/skills/creating-skills documents the default skills/ directory, with frontmatter entirely optional and name defaulting to the directory name — every field this projection emits is either read or ignored.
mcp	degraded	2026-09-06: the emitted document is read, and applied after a composite root's .mcp.json, "which wins on a server-name collision" — a server this bundle names identically to one there is overridden.
placeholders	supported	2026-09-06: https://docs.devin.ai/cli/extensibility/mcp/configuration states ${PLUGIN_ROOT} "expands to the plugin root like ${CLAUDE_PLUGIN_ROOT}", that ${PLUGIN_DATA} expands in args, env values, and cwd, that stdio processes "receive PLUGIN_ROOT and PLUGIN_DATA environment variables", and that cwd defaults to the plugin root with ./-prefixed commands resolved against it — the reserved behavior of Agent Plugins 1.0.0 §9.1.
hooks	unavailable	2026-09-06: Devin reads plugin hooks from a root hooks.json and documents them as "best effort and fail open" with SessionStart and SessionEnd excluded; Agent Plugins 1.0.0 defines no hooks, so this projection emits no hooks document for it to read.

Paths it reads: mcp.json, plugin.json, skills.
Per-file precedence: .devin-plugin/plugin.json (manifest, skills, mcp, placeholders), .claude-plugin/plugin.json (manifest, skills, mcp, placeholders).
Install: devin plugins install <plugin directory>.

Every row above is pinned to that client's own documentation on the date shown, is validated on every build, and renders in INSTALL.md and the generated hosts reference. A surface recorded unavailable or degraded names exactly what the client would need; no unsupported feature is projected silently.