First step toward `molecule connect <id>` — the out-of-box external-
runtime workspace connector specified in RFC #10.
What's in this PR (foundational, ~300 LOC of code + matching tests):
- `internal/backends.Backend` — the seam every concrete handler
implements: HandleA2A(ctx, Request) → Response, Close(). Two methods,
no inheritance, no surprise side effects. Concurrency-safe by
contract (poll dispatch may parallelise).
- Request/Response/Part/Config types — lossless JSON-RPC mirror so
backends can re-issue downstream without re-parsing.
- Compile-time registry — `Register("name", factory)` from each
backend's init(); `Build(name, cfg)` selects at runtime. Panics
on duplicate registration so drift fails loudly at startup, not
on first message.
- `mock` backend — single-template echo for CI smoke + tests + demos.
`--backend-opt reply="<template>"` with `%s` for inbound text.
- `molecule connect <workspace-id>` cobra command — flag surface,
validation, --dry-run for smoke. Loops (heartbeat, activity poll,
dispatch) land in M1.2 in internal/connect/.
Coverage:
- Registry: duplicate-name panic, empty-name panic, nil-factory panic,
Build unknown-name error includes registered list.
- Mock: default template, custom template, text-part concatenation,
Final=true on terminal response.
- Connect: --backend-opt KEY=VALUE parser (incl. value with =),
flag validation (missing token, bad mode, bad opt, unknown
backend), --dry-run happy path.
All tests pass under -race.
Out of scope (subsequent M1 PRs):
- M1.2: heartbeat + activity poll loops in internal/connect/
- M1.3: claude-code backend (wraps molecule-mcp-claude-channel)
- M1.4: GoReleaser tag-triggered release.yml workflow
RFC: https://github.com/Molecule-AI/molecule-cli/issues/10
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
