spec(port): port specs/port/trios-railway/crates/trios-railway-mcp/src/main.t27 (Closes #9776)

[dmitrii-f-t27]

Summary

Port gHashTag/trios-railway:crates/trios-railway-mcp/src/main.rs (at 8b229e9489ee, 114 lines) as specs/port/trios-railway/crates/trios-railway-mcp/src/main.t27 — Roadmap Stage 6 (goal #4548), target t27c gen-rust. Closes #9776.

The original is the public MCP server with dual transport: MCP over BOTH the modern Streamable HTTP transport (/mcp) and the legacy SSE transport (/sse + /message), with /healthz as the liveness probe, the IPv6 unspecified bind address for the Railway proxy, and the PORT fallback of 8080.

Per the issue's rule ("Port the decision, not the plumbing"), the three listed functions are ported under their names — main as an undefined; transport no test calls, root_handler and health_handler as the tested handler texts — and the decisions are ported with 5 tests (14 runtime asserts, 0 vacuous):

• resolve_listen_port / default_port — the PORT fallback: unset or unparseable falls back to 8080 (original lines 55-58);
• unspecified_bind_address — [::], so the IPv6-only Railway proxy reaches the server (lines 59-61);
• transport_count / mounted_route_count and the four route paths — the dual-transport route table: /mcp, /sse, /message, /healthz (lines 66-89);
• sse_keep_alive_secs — the 15-second SSE keep-alive (line 79); default_log_filter — the info default (lines 47-49);
• root_handler — the greeting naming both transports and where to reach them; health_handler — the ok liveness answer.

This PR supersedes #9846: its second commit (a helper rename) lacked the per-commit issue reference the L1 TRACEABILITY check requires, and rewriting pushed history needs a force-push this series never does — the same final file lands here as one commit with the reference.

Verification (all run live from the worktree root, zig 0.16.0)

• t27c parse: OK. t27c spec-status: IMPLEMENTED. t27c typecheck: 0 errors, 0 warnings.
• t27c coverage: 16/17 tested — only the main transport untested, by design.
• t27c test-report: 5 tests / 5 pass / 0 FAIL / 0 BLOCKED, 0 vacuous passes.
• t27c gen | grep -c 'not yet implemented': 0; gen | wc -l: 86 (> 12).
• grep -cE '^\s*(pub )?fn (main|root_handler|health_handler)\(': 3. grep -cE '^\s*test\s+(["|[A-Za-z_])': 5 (≥ 3).
• Boundary: git status --short — exactly this one file. The repo's lefthook pre-commit passed.
• dupe_scan: all 14 introduced names unique across 2040 specs (the helper names were checked BEFORE the commit — an earlier draft carried two colliding names, renamed here); main keeps its issue-mandated name, the 42-place pattern every port's entry point shares, with a non-identical body: the bare body scan adds no duplicate group (752 bodies / 221 groups on base, identical with this spec present).

Dmitrii Fedorov (@dmitrii-f-t27)

[dmitrii-f-t27]

@gHashTag Please merge this PR into master via the golden chain — rights on gHashTag/t27 are read-only for me (403), so the merge itself needs your action.

What this is: the #9776 port — crates/trios-railway-mcp/src/main.rs (gHashTag/trios-railway, at 8b229e9489ee, 114 lines) re-authored as specs/port/trios-railway/crates/trios-railway-mcp/src/main.t27. One file, one commit, head 76131bd6f, Closes #9776. This PR supersedes #9846, which I closed: its second commit (a helper rename) lacked the per-commit issue reference the L1 TRACEABILITY check requires, and this series does not force-push rewritten history — the identical final file lands here as one commit.

What is verified:

• t27c parse OK, spec-status IMPLEMENTED, typecheck 0 errors / 0 warnings, coverage 16/17 (only the main transport untested, by design), t27c test-report 5 tests / 5 pass / 0 FAIL / 0 BLOCKED, 0 vacuous — the 8080 port fallback, the [::] bind, the dual-transport route table (/mcp, /sse, /message, /healthz), the 15-second keep-alive, the info log filter, the greeting and the ok liveness answer.
• gen → 86 lines, 0 not yet implemented; the 3 required names count exactly 3; 5 test blocks; boundary exactly the one file.
• dupe_scan: all 14 introduced names unique across 2040 specs (checked before the commit); main keeps its issue-mandated name — the 42-place pattern every port's entry point shares — with a non-identical body; the bare body scan adds no duplicate group (752/221 unchanged).
• The t27b-native-run artifact of this head (commit 76131bd, run 39005752422): main.t27 row — reference pass, t27b pass, tests 5, invariants 0, asserts 14, blockers [], detail empty, reference_disagree: [].

CI (head 76131bd): required trio green — validate, check-linked-issue, parse-ratchet — and Check L1 TRACEABILITY green (the per-commit issue reference is present in the single commit); 26 checks pass overall, incl. emit-bitexact, t27b-native-linux, t27b-native-macos.

The 3 reds are the base-red trio, not this change: cli-tri (the #3324 include_str!), duplicate-bodies (only the known base names), t27b-native-ratchet (the same verdict red the Queen's port PRs carry; this spec's own row is reference pass + t27b pass — the registration debt is the UNLISTED class).

After the merge I will: verify the spec file live on the merge SHA, confirm #9776 auto-closed, and file the 14-step report.

Dmitrii Fedorov (@dmitrii-f-t27)