msd-core/docs/adr/959-capability-command-contribution.md

ADR-959: Capability Command Contribution

• Status: Accepted (graduated from Proposed by ADR-2346, 2026-07-17 — the cutover mechanism proven by full switch dissolution)
• Issue: #959
• Epic: #857 (Capability system) — rollout phase 4d
• Amends: ADR-894 (adds the deferred commands field)
• Realizes: ADR-857 decision 7 (in-tree code modules become Capabilities via an opened runCommand entrypoint)
• Builds on: ADR-0012 / ADR-0174 (CommandRoutingHub)

Context

ADR-857 decision 7 reserved a commands/module field so in-tree code modules (graphify, intel, audit) could "become Capabilities by registering their query family through an opened msd-tools.cjs entrypoint (registry) over the current hardcoded switch." ADR-894 fixed the capability.json format but deferred the commands field. This ADR designs it.

The current dispatch reality:

• runCommand is a 73-case hardcoded switch plus 12 route*Command family routers (init, config, phase, …). There is no registry table — every command-name → handler binding is hand-written.
• _dispatchNonFamily is a dead shim. It always returns false; its 10 call sites already pass { registryCommand, registryArgs, legacyCommand, legacyArgs } and fall through to the legacy CJS handler. Its own comment says it exists to "keep the helper contract so existing call sites remain unchanged during the phase sequence." It is the deliberately-prepared seam for registry dispatch.
• The CommandRoutingHub (ADR-0012, simplified by ADR-0174) is stateless. createHub({ cjsRegistry, manifest }) is constructed per dispatch with an inline family → subcommand → handler table and exposes only { dispatch }. There is no register() API and no persistent family registry. Each of the 12 routers builds a one-shot hub via routeHubCommandFamily and discards it. The hub's value is its uniform Result contract (UnknownCommand/InvalidArgs/HandlerRefusal/HandlerFailure), manifest-backed subcommand validation, arg-shape coercion, and observability.
• The registry and capability.json have no commands field today (confirmed absent).

Two distinct "command" kinds exist and must not be conflated: msd-tools CLI subcommands (internal, invoked by workflows via msd_run) and slash-commands/skills (commands/msd/*.md, agent-facing). This ADR is about the former — the CLI subcommand families that code-module features own. Skills are already a capability contribution (skills).

Decision

Core principle (grilled): the codebase already has the right abstraction — the router. The 12 route*Command functions each own a family's subcommand dispatch + arg parsing, and each already routes through the hub via routeCjsCommandFamily. A capability command family is therefore just a router, discovered via the registry instead of hardcoded into msd-tools' requires + switch. The registry's job is discovery, not re-implementing routing. This is the minimal change and reuses the proven abstraction wholesale — there is no new handler/arg convention.

1. A commands contribution on the feature role — no new role

A capability declares the CLI command families it owns, alongside its existing skills/agents/hooks/config contributions. No new role is introduced; a "code-module capability" is simply a feature whose primary contribution is commands rather than skills.

// capability.json (feature role) — new optional field
"commands": [
  {
    "family": "graphify",                  // the top-level msd-tools command this capability owns
    "module": "graphify.cjs",              // first-party in-tree module under msd-core/bin/lib/
    "router": "routeGraphifyCommand",      // exported router fn (same shape as the 12 host routers)
    "subcommands": ["query", "status"]     // OPTIONAL — doc/introspection metadata only; NOT used for dispatch
  }
]

• family — the top-level command string (single ownership across all capabilities).
• module — a first-party path resolved relative to msd-core/bin/lib/. Third-party / out-of-tree modules are out of scope (ADR-857 decision 7); they require their own trust/load ADR.
• router — the exported function with the standard router signature ({ args, cwd, raw, error }) => void — identical to routeInitCommand et al. It owns its own subcommand list, arg parsing, and defaultSubcommand internally, exactly as the 12 existing routers do.
• subcommands — optional, doc/introspection only; dispatch does not consult it (the router owns subcommand resolution).

2. The registry materializes a commandFamilies index

gen-capability-registry.cjs emits a discovery index — family → {capId, module, router} — no subcommand/handler enumeration (those live inside the router):

const commandFamilies = {
  "graphify": { capId: "graphify", module: "graphify.cjs", router: "routeGraphifyCommand" }
};

Added to module.exports alongside byLoopPoint, configKeys, etc.

3. Dispatch = invoke the registry-discovered router (which itself routes through the hub)

The capability's router is a standard route*Command: internally it calls routeCjsCommandFamily({ subcommands, handlers, … }) → routeHubCommandFamily → the per-call hub — exactly like the 12 existing routers. So "route through the hub" is satisfied by reuse, with zero new dispatch machinery and no registry-rebuilt handler table.

The dead _dispatchNonFamily(...) shim is replaced by a real dispatchCapabilityCommand({ command, args, cwd, raw }):

dispatchCapabilityCommand(command, args, cwd, raw):
  entry = registry.commandFamilies[command]        # guarded literal-key lookup
  if not entry: return false                        # → legacy fall-through (unchanged behavior)
  mod = require('./lib/' + entry.module)            # first-party, confined to bin/lib
  mod[entry.router]({ args, cwd, raw, error })      # the standard router signature
  return true

There is no new handler/arg convention: the capability author writes a router using the same routeCjsCommandFamily helper and the same per-subcommand parseNamedArgs/positional access the host routers use. The arg-parsing lives where it always has — inside the router — now owned by the capability.

4. Entrypoint placement: the default case

The registry dispatch is consulted in the default case of runCommand (unknown command), before the unknown-command error:

• An unmigrated command still hits its hardcoded case arm — untouched, behavior-identical.
• A migrated command's case arm is removed in its cutover PR, so the command now reaches default → dispatchCapabilityCommand → the capability handler.
• A command owned by no capability and no case → dispatchCapabilityCommand returns false → the existing unknown-command error.

This makes collision structurally impossible: a command is dispatched by its hardcoded case or the registry, never both (a case shadows default). The 10 existing _dispatchNonFamily call sites remain valid no-op seams and become the per-command migration points.

5. First-party only; third-party deferred

module is confined to msd-core/bin/lib/ and required in-process — the same trust level as the host's own handlers. Loading out-of-tree / third-party command modules carries a distinct trust/load/build/security surface and is deferred to its own ADR (mirroring the runtime third-party deferral in ADR-857 branch 8). The seam is built so that door can be opened later additively.

6. Staged rollout — graphify is the first real cutover (the pilot), not a synthetic fixture

A synthetic fixture proves the plumbing but not the model; only a real command exercises router extraction, the full capability bundle (command + skill + config gate + tier), and registry multiplicity. The maintainer also wants a user-testable artifact. So the pilot is a real cutover, chosen for minimum risk:

1. Build phase (4d-impl): add the commands schema + the commandFamilies index + the real dispatchCapabilityCommand in the default case, and cut over graphify as the first capability that owns a command family — in one cohesive migration:

   • a graphify capability bundling its command (family: graphify, a new first-party graphify-command-router.cjs extracted from the inline case sub-switch), its existing skill (commands/msd/graphify.md), its config gate (isGraphifyEnabled), and tier: full;
   • remove the case 'graphify': arm so dispatch flows default → registry → routeGraphifyCommand;
   • equivalence tests proving every graphify <sub> invocation (incl. the --budget flag and the hidden build snapshot) behaves identically old-path vs new-path.
   • graphify is the safest first target: zero workflow hot-path blast radius (no core workflow invokes it via bash — the skill drives it), smallest handler (496 LOC / 4 subcommands), already has a skill + cluster + config gate, and is full-only so the 4c install/surface consumption stays a no-op.

   This pilot is the phase-6 cutover template, executed once on a low-risk feature to surface integration surprises early.

2. Per-feature cutover (phase 6): repeat the graphify template for the remaining code-module features. intel goes last — a rollout finding: it has no skill and no cluster placement (invoked only from workflow bash), so it is not a clean capability and would need its skill/cluster created from scratch.

Validation invariants (enforced by the generator)

• Single family ownership — a family is owned by exactly one capability.
• First-party module — module resolves under msd-core/bin/lib/; no traversal.
• Router presence — router is a non-empty string; its existence as an export is verified at load (and may be lint-checked).
• Prototype-pollution guards at every dynamic-key site (the repo's CodeQL barrier), as with the other registry indexes.

Shadowing is not a generator concern (grilled). Because dispatch sits in the default case, a capability that names a still-live hardcoded command is harmless at runtime — the hardcoded case always wins and the capability command simply never dispatches. So no upfront HOST_RESERVED_COMMANDS list is maintained (it would be a real new maintenance surface for a problem the placement already neutralizes). The one moment it bites is a phase-6 cutover that adds the capability command but forgets to remove the old case (silent no-op). That is caught by a one-line cutover test ("command X now dispatches to capability Y"), not a build-time gate.

Alternatives considered

1. Registry rebuilds the hub handler table (subcommands:[{name,export}] → per-call hub). Rejected after grilling: this re-implements, in the registry + dispatcher, what a route*Command already does (subcommand list, handler wiring, arg parsing, defaultSubcommand). Discovering a standard router instead keeps the existing abstraction intact, removes the need for the registry to know subcommands/exports, and dissolves any "new handler/arg convention." The chosen design routes through the hub because the discovered router does (via routeCjsCommandFamily) — satisfying the hub decision with zero new dispatch machinery.
2. Direct byCommand → module.export dispatch (bypass the hub entirely). Rejected (maintainer choice): the discovered-router path already routes through the hub (ADR-0174's uniform Result/manifest/observability) and stays consistent with the 12 family routers.
3. A new persistent hub registry (hub.register(family, handlers)). Rejected: the hub is intentionally stateless (ADR-0012/0174); introducing a singleton mutable registry contradicts that design and is unnecessary — a registry-discovered router constructs its own per-call hub exactly as today.
4. A generator HOST_RESERVED_COMMANDS shadowing gate. Rejected after grilling: the default-case placement makes shadowing harmless at runtime, so an upfront host-reserved list is a maintenance surface for a neutralized problem. A one-line cutover test covers the only failure mode (forgetting to remove a migrated case).
5. A new role: code-module/tool. Rejected: commands are just another contribution kind on a feature; a separate role adds taxonomy without behavior.
6. Migrate the 73 hardcoded cases now. Rejected: that is the per-feature cutover (phase 6). Build the mechanism + a synthetic pilot first (registry-only), proven behavior-preserving — the rollout's consistent pattern.
7. Open the entrypoint at each _dispatchNonFamily call site (not default). Rejected as the primary placement: the default-case approach makes collision structurally impossible and keeps unmigrated commands on their exact current path. The per-case shims remain as migration markers.

Consequences

• Positive: code-module features can own CLI command families declaratively; the hardcoded switch shrinks one command at a time at cutover; dispatch reuses the audited hub contract; the third-party door is left openable additively; the graphify pilot is a tangible, testable plug-in and the proven phase-6 template.
• Negative / cost: a second dispatch path (registry default-case) coexists with the 73-case switch until migrations complete; a capability command family is a first-party router the author must write to the existing route*Command shape (no new convention, but it is real code the registry only discovers); the pilot is a real migration, so graphify's dispatch path changes (equivalence-proven) rather than being a pure no-op.
• Neutral: every non-migrated command stays on its exact current case path; the registry-default seam is dormant for them.

Out of scope

The build (4d-impl); migrating commands other than the graphify pilot; third-party / out-of-tree command modules; phase 5 (runtime descriptors); the remaining phase-6 per-feature cutovers.

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Amendment — 2026-07-17 (ADR-2346): Status Proposed → Accepted

This ADR's mechanism — "a capability command family is just a router, discovered via the registry instead of hardcoded," consulted in runCommand's default case — is accepted. The proof is ADR-2346 (epic #2345), which completes the cutover and dissolves the 73-case switch entirely into a two-layer dispatch (registry for families + a leaf-verb table filling the _dispatchNonFamily seam this ADR named). ADR-2346 records the two decisions this ADR deliberately left open (full dissolution; where leaf verbs belong); it does not alter this ADR's mechanism, the commands contribution field, or the default-case placement that makes collision structurally impossible. See ADR-2346.