agentic-mobile-control/openspec/changes/skill-catalog-subscription/design.md

Context

This builds on the apex-agent-mvp change (currently proposed, not yet applied), which establishes the Device/Driver/Perception/Agent-Runtime/MCP layers for Apex Agent. That change already defines an MCP Tool Server (api/mcp.py) exposing device capabilities; this change adds a parallel skills/ package and new MCP tools onto the same server, without touching the device/perception/runtime code.

The key external constraint: skill authoring, versioning, and entitlement live in a separate, already-planned Subscription Platform (a distinct information-management system, out of scope here). Apex Agent is a consumer of that platform's catalog, not the source of truth for skill content. We only control: how Apex Agent stores what it has synced, how it exposes that to the LLM via MCP, and the contract it expects the Subscription Platform to satisfy.

Two kinds of Skill must be supported, per product direction:

• Knowledge skill: free-form structured instructional content (markdown/text + metadata) the LLM reads to decide how to act — e.g. "tips for searching effectively on Xiaohongshu." The LLM still plans/executes via the existing agent-runtime/tools layer.
• Flow-template skill: a predefined, parameterized sequence of capability calls (tap/swipe/input steps with placeholders, e.g. {query}), which the LLM mostly fills in and triggers rather than re-planning from scratch.

Goals / Non-Goals

Goals:

• Define a single Skill data model general enough to represent both knowledge and flow-template skills with shared metadata (id, name, description, version, tags, subscription/source id).
• Expose skills to the LLM through MCP tools that are indistinguishable in style from the existing device tools (semantic, driver/platform-agnostic).
• Define a clear, minimal contract for what Apex Agent needs from the Subscription Platform: a way to fetch "skills I'm entitled to" and a way to learn about changes (poll or push), without dictating that platform's internal design.
• Enforce subscription-based visibility so list_skills/search_skills/get_skill only ever surface skills the current deployment (tenant/device/agent) is actually subscribed to.
• Let a flow-template skill's steps execute through the existing tools/ functions from apex-agent-mvp (no new execution primitives) — a flow template is just a data-driven script over the same capability calls the Executor already uses.

Non-Goals:

• Designing or implementing the Subscription Platform itself (its UI, billing, authoring workflow, or storage).
• Automatic skill generation/authoring by the LLM.
• A full permission/RBAC system — subscription visibility is scoped to "is this skill in my entitled set," not fine-grained per-user roles.
• Real-time push infrastructure (websockets/queues) as a hard requirement — push is supported as an optional transport; polling sync must work standalone.
• Executing flow-template skills with a new engine — they are interpreted by the existing runtime/executor.py, not a separate workflow engine.

Decisions

D1: Skill is a single model with a kind discriminator (knowledge | flow_template), not two unrelated types

Both kinds share SkillMetadata (id, name, description, version, tags, source/subscription id, updated_at). A KnowledgeSkill carries content (markdown/text). A FlowTemplateSkill carries steps (ordered list of {tool, args_template}, where args_template values may contain {param} placeholders) and a parameters schema (name, type, required, description) used to validate/prompt for inputs before execution.

• Alternative considered: Two entirely separate catalogs/tables/tool sets for knowledge vs. flow skills. Rejected — list_skills/search_skills would need to be duplicated, and most metadata (id/name/description/version/tags) is identical; a discriminated union keeps one catalog and one set of list/search tools while get_skill returns kind-specific content.

D2: Skill Catalog is a local, read-mostly cache; Subscription Platform is always the source of truth

skills/catalog.py stores the last-synced copy of entitled skills locally (for offline availability and low-latency MCP responses) but never treats local edits as authoritative — there is no "create/update skill" MCP tool or API in this change. All content changes flow one direction: Subscription Platform → sync client → local catalog.

• Alternative considered: Let Apex Agent locally override/edit synced skills. Rejected — breaks the "another system manages skills" requirement from the proposal and creates drift/merge-conflict problems with no clear owner.

D3: Sync client supports pull (poll) as the required baseline, push (webhook) as an optional accelerator

skills/sync_client.py defines a fetch_entitled_skills(subscription_id, since_version) contract against the Subscription Platform's assumed API, called on a configurable interval (baseline). If the platform can also deliver change notifications (webhook/callback), an optional receiver triggers an immediate out-of-cycle fetch instead of waiting for the next poll — but correctness never depends on push arriving.

• Alternative considered: Push-only (webhook-driven) sync. Rejected — makes Apex Agent's catalog freshness dependent on network reachability of an inbound webhook, which is operationally harder (firewalls/NAT) than Apex Agent making outbound poll requests; poll-as-baseline is strictly more deployable.

D4: Subscription-based visibility is enforced at the catalog query layer, not just at sync time

Even though sync only ever pulls "entitled" skills, skills/catalog.py's query functions (used by both MCP tools and any future internal caller) re-check that a skill's subscription id is still in the caller's active subscription set at query time, not just at last-sync time. This guards against a stale local cache still containing a skill whose entitlement was revoked but not yet re-synced.

• Alternative considered: Trust the local cache fully between syncs (no re-check at query time). Rejected — entitlement revocation should not have to wait for the next poll interval to stop being visible if the revocation is already known locally (e.g. via a push notification that only carries "removed" without full content).

D5: Flow-template skills execute via existing tools//runtime/executor.py, with a resolution step in between

skills/mcp_tools.py exposes get_skill (returns metadata + content/template) and a parameter-resolution helper; it does not expose a run_skill tool that silently executes on the LLM's behalf. The LLM fetches the flow template, fills placeholders itself (or asks the user for missing required parameters), and then issues the already-existing device-capability tool calls (tap, input_text, etc.) from apex-agent-mvp in the order/values the template specifies.

• Alternative considered: Add a single run_skill_flow(skill_id, params) MCP tool that executes the whole sequence server-side. Rejected for this change — it would bypass the Agent Runtime's Observe→Think→Act loop and Executor retry/wait logic from apex-agent-mvp, silently skipping Scene verification between steps. Keeping execution inside the existing loop (LLM issues each tool call itself, informed by the template) preserves the "AI decides based on what it currently observes" principle the whole platform is built on. A batched execution helper can be revisited later as a design decision in its own change if needed.

Risks / Trade-offs

• [Risk] The Subscription Platform's actual API shape is unknown/assumed (fetch_entitled_skills, optional webhook) → Mitigation: keep skills/sync_client.py behind a small internal interface (similar to Driver in apex-agent-mvp) so the concrete HTTP client can be adjusted once the real Subscription Platform API is finalized, without touching catalog.py or mcp_tools.py.
• [Risk] Stale cache could serve outdated skill content between polls → Mitigation: D4's query-time entitlement re-check plus a configurable poll interval; document the staleness window explicitly rather than promising real-time freshness.
• [Risk] Flow-template skills reference tools/parameters that drift from the actual tools/ function signatures in apex-agent-mvp (e.g. a template calls a tool that was renamed) → Mitigation: validate a flow template's tool names against the currently registered MCP/tool set at sync time (or at least at get_skill time) and surface a clear "skill unavailable/invalid" error rather than letting a bad call reach the device.
• [Trade-off] No local skill authoring/editing keeps this change simple and avoids ownership ambiguity, but means Apex Agent is fully dependent on the Subscription Platform being reachable at least once to have any skills at all — acceptable since the platform is a required dependency by design, not an optional enhancement.
• [Trade-off] Not providing a server-side run_skill_flow execution tool keeps flow templates consistent with the Observe-Think-Act loop, at the cost of the LLM needing a few more tool-call round trips per flow skill than a single batched call would take — acceptable given the platform's core principle of always re-observing between actions.

Migration Plan

Additive only: new skills/ package, new MCP tools, and new local storage tables/files. No existing apex-agent-mvp code paths are modified (only composed with, per D-decisions above). If apex-agent-mvp has already been applied, this change's MCP tools register onto its existing MCP server instance; if not yet applied, skills/mcp_tools.py can stand up its own MCP server instance for independent testing and be merged once apex-agent-mvp lands. Rollback is simply removing the skills/ package and its MCP tool registrations; no data migration or schema changes to existing tables are required.

Open Questions

• Exact Subscription Platform API contract (auth mechanism, request/response shapes, whether it supports since_version incremental sync or only full-catalog fetch) — to be confirmed with that platform's team/spec before skills/sync_client.py is finalized; this design assumes an interface shape that can absorb either.
• Whether flow-template args_template placeholders need a richer expression language (e.g. simple conditionals) or plain {param} substitution is sufficient for the MVP — left open, default to plain substitution and revisit if a real skill needs more.
• Where the local Skill Catalog lives relative to apex-agent-mvp's existing SQLite task-metadata DB (same DB file, new tables, vs. a separate DB/file) — deferred to implementation time in tasks.md, doesn't affect the capability contracts defined here.