M1 slice 1: amicode service — extension-host /amicode/profile with fork-parity fixtures

[aarontrowbridge]

Part of #451 (M1 — extension-host amicode service, slice 1 of the route port; not closing).

What's here

The first vertical slice of the M1 extension-host service — the layer that replaces the fork server's /amicode/* routes at cutover (M0 gate (a): canonical opencode ships no custom routes):

• src/amicode_service/server.ts — framework-free node:http server on 127.0.0.1 (ephemeral port), per-boot Basic auth using the SAME mint + header as the opencode spawn (server_auth.ts), exact-match route table mirroring the fork's router.add mounts, never-reject handlers (the fork's collapse-into-one-shape discipline). vscode-free so it boots in-process under vitest.
• src/amicode_service/profile.ts + roots.ts — near-verbatim port of the fork's profile.ts @ v1.18.10-amicode.11: graceful identity synthesis (name from the personal vault mount when the profile lacks one), platform-mix focus line, live "Amico remembers" ranking, 10s response cache, and the query-param POST contract (fields ride the URL, not a JSON body — a detail a naive port would silently break). One documented superset: AMICODE_MOUNTS_FILE as a test seam (unset → fork-identical).
• scripts/record_amicode_fixtures.mjs + scripts/amicode_fixture_seed.mjs — the golden-fixture recorder: boots the vendored fork binary against a deterministic seeded sandbox (unequal platform counts so sort order can't depend on readdir; pinned note mtimes) and records request/response pairs. Run by hand; CI replays committed fixtures without the binary.
• test/amicode_service_profile.test.ts — the parity proof: same seed, boot the PORT, replay every recorded request, require deep-equal responses.

The recorded arc

Cold read (synthesized identity + stats + remembers) → edit focus → clear name (the mounts.toml fallback fires: "Test Personal") → warm read. All four byte-deep-equal between fork binary and port.

Verification

• pnpm vitest run test/amicode_service_profile.test.ts — 7/7 (4 golden replays + pin-metadata + 401 + 404)
• pnpm test — 94 files, 1061/1061
• pnpm typecheck — clean

Pattern for the remaining 17 modules

Each port slice: port the module(s) → extend the recorder's request list → re-record → contract test replays. Route count: 1 of 31 mounted (2 of 31 routes).

Not in this slice (deliberately)

Extension activation wiring (nothing consumes the service until the widget-frame slice moves consumers to it), CSP/origin widening, the ?auth_token= iframe flow.

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