feat(metaharness): AnyHarness metaharness skeleton + playground demo (W4)

[espetro]

Summary

Workstream W4 from .agents/plans/2026-10-07-v2-foundation.md: the AnyHarness metaharness skeleton — the minimal reference harness consumed entirely through our own extension model, doubling as e2e playground + SDK-outreach demo.

Follows the calca @calca/agent-core contract-seam precedent (harness.ts ~59 LOC): AgentHarness / AgentSpec / Capabilities / HarnessRunInput, AI SDK ToolLoopAgent as the loop, capability injection where exec/fs/mcp slots are computer-only.

Changes

packages/metaharness/ (@any-harness/metaharness)

• src/harness.ts — contract seam: AgentHarness, AgentSpec, Capabilities, HarnessRunInput, StoragePort, SecretPort (BYOK), ExecPort (computer-only slot)
• src/bridge.ts — bridge protocol v0.1 client surface: BridgeOps table typing all 8 pinned ops (capabilities.negotiate, extensions.list, extensions.get, hooks.invoke, commands.resolve, skills.materialize, tools.call, events.notify), BridgeClient, inProcessBridge() in-process binding, Extension/ExtensionKind/ManifestRef interface pins
• src/ai-sdk.ts — aiSdkHarness(), ToolLoopAgent adapter forwarding per-run Capabilities into each tool's options.context
• src/tools.ts — extensionTools(): bridge surfaces (list_extensions, get_extension, call_extension_tool, resolve_command, materialize_skill) + computer_exec; every execute reads capabilities from options.context — absent slots degrade instead of #ifdefing
• src/harness.test.ts — 4 vitest cases on MockLanguageModelV4: text streaming, capability injection via tool context, bridge tool wiring, computer-only degradation
• AGENTS.md — seam rules (isomorphic, interface-first, no harness logic, capabilities not globals)

apps/playground/ (@any-harness/playground)

• src/cli.ts — one-shot (--prompt) + REPL entry; the only file with node:* imports (argv/readline/stdout)
• src/capabilities.ts — unstorage fs storage, BYOK SecretPort over injected env, stubbed computer-only exec
• src/host.ts — in-process demo bridge host with canned extensions (commit-smith skill, echo-mcp MCP, review command)
• src/model.ts — createOpenAICompatible over AI_BASE_URL/AI_API_KEY/AI_MODEL_ID
• src/run.ts — streamTurn() normalizing stream parts for display

Test plan

• pnpm --filter @any-harness/metaharness test — 4/4 pass
• tsc --noEmit clean in metaharness + playground (stub packages have no tsconfig — pre-existing)
• E2E: one-shot + REPL runs against an OpenAI-compatible endpoint — model calls list_extensions / call_extension_tool through the in-process bridge and renders results
• Capability matrix updated (if adapter behaviour changed) — n/a
• Linked to a refined issue in Project 14

Notes

• Bridge client is in-process only; stdio/HTTP-loopback transports come with the W3 spec + sdk host. demoBridge() is canned data, not a store.
• Deps: ai (catalog) in metaharness; playground adds unstorage (catalog) + @ai-sdk/openai-compatible@^3 — the one non-catalog dep, justified: ai ships no provider adapter and BYOK demo needs one. @ai-sdk/provider is devDep-only (test types for the mock model).
• pnpm test at root still fails on the cli/sdk/spec stubs ("no test files") — pre-existing scaffold state, CI marks test continue-on-error.
• pnpm-lock.yaml committed (repo had none; CI installs --frozen-lockfile).

Link to Devin session: https://app.devin.ai/sessions/fd3e78041312436aa9f8d235e293d94a
Open in Devin Desktop: https://app.devin.ai/desktop/session/fd3e78041312436aa9f8d235e293d94a?variant=devin
Requested by: @espetro

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

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[cursor]

Approved. Cursor Bugbot was not present on this PR after the first check poll, so that signal was skipped; no applicable approval policy requires human review, and there are no unresolved automated findings. Human review is not required for merge gating from this automation.

  

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