What the next program says the language needs

Status: DONE 2026-08-04. Program: HTTP key-value server (tools/tycho-kvsrv/). Outcome: 2 phases complete — actor store + daemon gate (make kvsrv-check, ci step [3l/18]); no language findings.

This plan is a fresh clone, 2026-08-04: the completed tycho-rsa plan lives at docs/internals/plan-tycho-rsa-DONE.md. The rule from that plan holds here: *does anything that is not the program written to want it need this?* A finding becomes a phase only when a second, independent caller exists.

The program -- the HTTP key-value server (tools/tycho-kvsrv/)

A concurrent HTTP server exposing a key-value store: GET/PUT/DELETE /kv/<key>, keep-alive connections, status codes, over core:net + core:httpd. The stress is networking plus the shared-state concurrency question.

Rule: there is no shared mutable storage and no lock machinery — race freedom is by construction. The store is therefore an ACTOR: one task owns the map, and connection handlers reach it through channels. The channel topology follows from the affine/non-storable rules (a Channel cannot be a struct field, a container element, or a return): ONE shared command channel whose payload carries a worker id, plus one NAMED reply channel per worker, passed as spawn arguments — so every channel has exactly one receiver and nothing races. The worker count is a named constant (4); the worker pool uses tycho-httpd's proven recursive fan-out on the one shared listening fd.

The differential is the daemon-testing pattern from server/run.sh: start with --port 0, poll the stderr banner for the real port, drive it with a raw-socket python client, assert the responses. The gate asserts the round-trips (PUT/GET/DELETE, 404 on a missing key), keep-alive (two requests, one connection), a method/path 405/404, and the concurrency probe: 4 parallel clients PUT distinct keys, all 4 come back intact (the actor serializes the map; the assertion proves no command is dropped).

Scope: the store is IN-MEMORY (no persistence — the B+ tree lives in the tycho-kv tool and is not a corelib).

Phases

Phase 1 -- the server: routes, the actor store, the worker pool [DONE 2026-08-04]

The server is ~240 lines: core:httpd for request parsing and response rendering, core:net for the fds, and the concurrency shape the language requires: the store is an ACTOR (one task owns the [string: string] map), reachable through ONE shared command channel whose payload carries the worker id, plus four NAMED reply channels passed as spawn arguments. The rules that require this: a Channel cannot be a struct field (compiler-rejected with a clean diagnostic), a container element, or a return value; tasks cannot detach (implicit join at scope exit). The worker pool is tycho-httpd's recursive fan-out over the one shared listening fd, four workers, each serving its accepted connection inline.

Every channel has exactly one receiver, so nothing can race -- by construction, not by lock. The gate proves the actor round-trip under interleaving: 4 parallel clients PUT distinct keys and all 4 come back intact.

Phase 2 -- the daemon gate [DONE 2026-08-04]

make kvsrv-check (ci step [3l/18], ~2s) follows the server/run.sh daemon pattern: start with --port 0, poll the stderr banner for the bound port (the socket is already listening, so the runner never sleeps a fixed interval), drive it with one raw-socket python client, assert: the round-trips (PUT/GET/DELETE, 404 on a missing key), the protocol (POST 405, a non-kv path 404), keep-alive (two requests on one connection, both answered), and the concurrency probe -- all golden-locked.

No findings to file. The networking and shared-state-concurrency axes held: the actor shape follows from the documented channel rules, race freedom came free, and the only surprise was in the test client (a python client that forgot the blank line after the request head -- the server correctly waited for it).

Findings

(none -- findings appear here as the program is written)

Phases

(none -- a finding becomes a phase only when a second, independent caller needs it)