diff --git a/specs/port/trios-railway/crates/trios-railway-mcp/src/main.t27 b/specs/port/trios-railway/crates/trios-railway-mcp/src/main.t27
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+// trios-railway-mcp — the public MCP server with dual transport.
+// Port of gHashTag/trios-railway:crates/trios-railway-mcp/src/main.rs
+// (at 8b229e9489ee, 114 lines) — Roadmap Stage 6, goal #4548, target
+// t27c gen-rust.
+//
+// The original serves MCP (Model Context Protocol) over BOTH the modern
+// Streamable HTTP transport (/mcp) and the legacy SSE transport
+// (/sse + /message), with /healthz as the liveness probe and / as the
+// greeting. It binds on the IPv6 unspecified address so the Railway
+// IPv6-only private-network proxy can reach it, reads the port from the
+// environment defaulting to 8080, keeps the SSE stream alive every 15
+// seconds, defaults the log filter to "info", prints one boot line
+// before tracing starts (R5: never silent), and shuts down gracefully
+// on the interrupt signal.
+//
+// The servers, the router and the signal handling are plumbing; the
+// decisions — the port fallback, the bind address, the route table with
+// its two transports and four routes, the keep-alive interval, the
+// default log filter, and the two handler texts — are ported here as
+// pure functions and tested. The main transport keeps its name with an
+// `undefined;` body that no test calls (issue #9776, "Port the decision,
+// not the plumbing").
+
+module port::trios_railway_mcp_main;
+
+// ---------------------------------------------------------------------------
+// Original lines 39-105: `async fn main() -> Result<()>`. The boot: bind,
+// mount both transports, serve with graceful shutdown. Pure transport;
+// its decisions are ported below.
+// ---------------------------------------------------------------------------
+
+pub fn main() -> ?str {
+    return undefined; // plumbing: the dual-transport server boot and serve loop (lines 39-105)
+}
+
+// Original lines 55-58: the PORT environment read with the 8080
+// fallback — unset or unparseable falls back, per the presence flag.
+pub fn default_port() -> u16 {
+    return 8080;
+}
+
+pub fn resolve_listen_port(port_set: bool, port: u16) -> u16 {
+    if (!port_set) {
+        return default_port();
+    }
+    return port;
+}
+
+// Original lines 59-61: bind on the IPv6 unspecified address so the
+// Railway IPv6-only private-network proxy reaches the server.
+pub fn unspecified_bind_address() -> str {
+    return "[::]";
+}
+
+// Original lines 66-89: two transports (Streamable HTTP on /mcp, legacy
+// SSE on /sse + /message) and the /healthz liveness probe — four routes
+// in all.
+pub fn transport_count() -> usize {
+    return 2;
+}
+
+pub fn mounted_route_count() -> usize {
+    return 4;
+}
+
+pub fn mcp_path() -> str {
+    return "/mcp";
+}
+
+pub fn sse_path() -> str {
+    return "/sse";
+}
+
+pub fn message_path() -> str {
+    return "/message";
+}
+
+pub fn healthz_path() -> str {
+    return "/healthz";
+}
+
+// Original line 79: the SSE keep-alive interval.
+pub fn sse_keep_alive_secs() -> u64 {
+    return 15;
+}
+
+// Original lines 47-49: the log filter defaults to "info" when the
+// environment carries no valid filter.
+pub fn default_log_filter() -> str {
+    return "info";
+}
+
+// ---------------------------------------------------------------------------
+// Original lines 107-110: `async fn root_handler() -> &'static str` —
+// the greeting names both transports and where to reach them.
+// ---------------------------------------------------------------------------
+
+pub fn root_handler() -> str {
+    return "trios-railway-mcp: public MCP server for the IGLA project.\nPOST JSON-RPC to /mcp (Streamable HTTP) or connect to /sse (legacy SSE)\n";
+}
+
+// ---------------------------------------------------------------------------
+// Original lines 112-114: `async fn health_handler() -> &'static str` —
+// the liveness answer.
+// ---------------------------------------------------------------------------
+
+pub fn health_handler() -> str {
+    return "ok";
+}
+
+// ---------------------------------------------------------------------------
+// Tests: every decision above asserted against values read from the
+// original. No test calls the main transport.
+// ---------------------------------------------------------------------------
+
+test health_answers_ok {
+    assert(health_handler() == "ok");
+}
+
+test root_greeting_names_both_transports {
+    assert(root_handler() == "trios-railway-mcp: public MCP server for the IGLA project.\nPOST JSON-RPC to /mcp (Streamable HTTP) or connect to /sse (legacy SSE)\n");
+}
+
+test port_defaults_and_overrides {
+    assert(default_port() == 8080);
+    assert(resolve_listen_port(false, 0) == 8080);
+    assert(resolve_listen_port(true, 9000) == 9000);
+}
+
+test bind_and_route_layout {
+    assert(unspecified_bind_address() == "[::]");
+    assert(transport_count() == 2);
+    assert(mounted_route_count() == 4);
+    assert(mcp_path() == "/mcp");
+    assert(sse_path() == "/sse");
+    assert(message_path() == "/message");
+    assert(healthz_path() == "/healthz");
+}
+
+test keep_alive_and_log_filter {
+    assert(sse_keep_alive_secs() == 15);
+    assert(default_log_filter() == "info");
+}