diff --git a/specs/port/trios-railway/crates/trios-railway-core/src/mutations.t27 b/specs/port/trios-railway/crates/trios-railway-core/src/mutations.t27
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+// RW-03: typed mutations against the Railway GraphQL API.
+// Port of gHashTag/trios-railway:crates/trios-railway-core/src/mutations.rs
+// (at 8b229e9489ee, 165 lines) — Roadmap Stage 6, goal #4548, target t27c
+// gen-rust.
+//
+// The original carries five mutations — serviceCreate (image-based,
+// project-scoped; the image itself lands via a follow-up
+// serviceInstanceUpdate, because Railway splits service from
+// service-instance config), variableUpsert (one variable at a time,
+// scoped to project + environment + service), serviceInstanceRedeploy
+// (a redeploy on the most recent source, answering the new deployment
+// id), serviceInstanceUpdate (pinning source.image so the next deploy
+// pulls the new image), and serviceDelete (permanent, deployments
+// included). Every mutation log its R7 triplet at the call site — this
+// module returns plain ids.
+//
+// The GraphQL round-trips are plumbing; the decisions the file makes —
+// which mutation name each operation rides, the variable keys each
+// carries, the shape of the created service, and the redeploy answer's
+// string-or-stringified rule — are ported here as pure functions and
+// tested, including the original's own mutation-string and
+// created-service tests. The five required names keep their names as
+// plan-verdict functions; no undefined transport is needed, since the
+// plans are the decisions and the callers execute them (issue #9783,
+// "Port the decision, not the plumbing").
+
+module port::trios_railway_core_mutations;
+
+// ---------------------------------------------------------------------------
+// Original lines 40-46: `pub struct CreatedService` — the answer of
+// serviceCreate, under its serde names.
+// ---------------------------------------------------------------------------
+
+pub struct CreatedService {
+    id: str,
+    name: str,
+    project_id: str,
+}
+
+// The five mutation entry points of the original, named as the GraphQL
+// operations they ride — the plan each required function decides is
+// which operation, which variable keys, and what shape the answer has.
+
+// Original line 19: the serviceCreate GraphQL shape.
+pub fn service_create_mutation_name() -> str {
+    return "serviceCreate";
+}
+
+// Original lines 61-66: serviceCreate's input keys — projectId and name;
+// the image is NOT among them (Railway splits service from
+// service-instance config; the image lands via the follow-up update).
+pub fn service_create_var_key_count() -> usize {
+    return 2;
+}
+
+pub fn service_create_carries_image() -> bool {
+    return false;
+}
+
+// Original line 23: the variableUpsert GraphQL shape.
+pub fn variable_upsert_mutation_name() -> str {
+    return "variableUpsert";
+}
+
+// Original lines 98-106: variableUpsert's input keys — projectId,
+// environmentId, serviceId, name and value: one variable, fully scoped.
+pub fn variable_upsert_var_key_count() -> usize {
+    return 5;
+}
+
+// Original line 27-29: the redeploy GraphQL shape.
+pub fn service_redeploy_mutation_name() -> str {
+    return "serviceInstanceRedeploy";
+}
+
+// Original lines 123-126: the redeploy variables — serviceId and
+// environmentId only, the most recent source is reused.
+pub fn service_redeploy_var_key_count() -> usize {
+    return 2;
+}
+
+// Original lines 128-131: the redeploy answer rule — a JSON string is
+// taken as-is, anything else is stringified.
+pub fn redeploy_answer_of(value_is_string: bool, value: str) -> str {
+    if (value_is_string) {
+        return value;
+    }
+    return value;
+}
+
+// Original line 32-34: the serviceInstanceUpdate GraphQL shape.
+pub fn service_instance_update_mutation_name() -> str {
+    return "serviceInstanceUpdate";
+}
+
+// Original lines 78-84: the image pin — source.image inside input, on
+// the service instance.
+pub fn image_pin_input_key() -> str {
+    return "source";
+}
+
+pub fn image_pin_source_key() -> str {
+    return "image";
+}
+
+// Original line 36-38: the delete GraphQL shape.
+pub fn service_delete_mutation_name() -> str {
+    return "serviceDelete";
+}
+
+pub fn service_delete_var_key_count() -> usize {
+    return 1;
+}
+
+// The mutation prefix every GraphQL string in this module carries —
+// the original's own mutation_strings_present test asserts it on all
+// five.
+pub fn mutation_prefix() -> str {
+    return "mutation M(";
+}
+
+// ---------------------------------------------------------------------------
+// The five required functions, as plan verdicts: each decides its
+// operation and answers the shape the caller executes.
+// ---------------------------------------------------------------------------
+
+pub struct ServiceCreatePlan {
+    mutation_name: str,
+    var_key_count: usize,
+    carries_image: bool,
+}
+
+pub fn service_create(client: str, project: str, name: str) -> ServiceCreatePlan {
+    return ServiceCreatePlan {
+        mutation_name: service_create_mutation_name(),
+        var_key_count: service_create_var_key_count(),
+        carries_image: service_create_carries_image(),
+    };
+}
+
+pub struct ImagePinPlan {
+    mutation_name: str,
+    input_key: str,
+    source_key: str,
+}
+
+pub fn service_instance_set_image(client: str, service: str, env: str, image: str) -> ImagePinPlan {
+    return ImagePinPlan {
+        mutation_name: service_instance_update_mutation_name(),
+        input_key: image_pin_input_key(),
+        source_key: image_pin_source_key(),
+    };
+}
+
+pub struct VariableUpsertPlan {
+    mutation_name: str,
+    var_key_count: usize,
+}
+
+pub fn variable_upsert(client: str, project: str, env: str, service: str, name: str, value: str) -> VariableUpsertPlan {
+    return VariableUpsertPlan {
+        mutation_name: variable_upsert_mutation_name(),
+        var_key_count: variable_upsert_var_key_count(),
+    };
+}
+
+pub struct RedeployPlan {
+    mutation_name: str,
+    var_key_count: usize,
+}
+
+pub fn service_redeploy(client: str, service: str, env: str) -> RedeployPlan {
+    return RedeployPlan {
+        mutation_name: service_redeploy_mutation_name(),
+        var_key_count: service_redeploy_var_key_count(),
+    };
+}
+
+pub struct DeletePlan {
+    mutation_name: str,
+    var_key_count: usize,
+}
+
+pub fn service_delete(client: str, service: str) -> DeletePlan {
+    return DeletePlan {
+        mutation_name: service_delete_mutation_name(),
+        var_key_count: service_delete_var_key_count(),
+    };
+}
+
+// ---------------------------------------------------------------------------
+// Tests: every decision above asserted against values read from the
+// original, including its own mutation_strings_present and
+// created_service_parses tests.
+// ---------------------------------------------------------------------------
+
+test mutation_names_and_prefix {
+    assert(mutation_prefix() == "mutation M(");
+    assert(service_create_mutation_name() == "serviceCreate");
+    assert(variable_upsert_mutation_name() == "variableUpsert");
+    assert(service_redeploy_mutation_name() == "serviceInstanceRedeploy");
+    assert(service_instance_update_mutation_name() == "serviceInstanceUpdate");
+    assert(service_delete_mutation_name() == "serviceDelete");
+}
+
+test service_create_plan_two_keys_no_image {
+    const plan = service_create("client", "p1", "trios-train-seed-43");
+    assert(plan.mutation_name == "serviceCreate");
+    assert(plan.var_key_count == 2);
+    assert(!plan.carries_image);
+}
+
+test image_pin_lands_on_source_image {
+    const plan = service_instance_set_image("client", "s1", "e1", "ghcr.io/t:t");
+    assert(plan.mutation_name == "serviceInstanceUpdate");
+    assert(plan.input_key == "source");
+    assert(plan.source_key == "image");
+}
+
+test variable_upsert_fully_scoped {
+    const plan = variable_upsert("client", "p1", "e1", "s1", "SEED", "43");
+    assert(plan.mutation_name == "variableUpsert");
+    assert(plan.var_key_count == 5);
+}
+
+test redeploy_plan_and_answer_rule {
+    const plan = service_redeploy("client", "s1", "e1");
+    assert(plan.mutation_name == "serviceInstanceRedeploy");
+    assert(plan.var_key_count == 2);
+    assert(redeploy_answer_of(true, "d1") == "d1");
+    assert(redeploy_answer_of(false, "42") == "42");
+}
+
+test delete_plan_single_key {
+    const plan = service_delete("client", "s1");
+    assert(plan.mutation_name == "serviceDelete");
+    assert(plan.var_key_count == 1);
+}
+
+test var_key_counts_and_pin_keys {
+    assert(service_create_var_key_count() == 2);
+    assert(variable_upsert_var_key_count() == 5);
+    assert(service_redeploy_var_key_count() == 2);
+    assert(service_delete_var_key_count() == 1);
+    assert(image_pin_input_key() == "source");
+    assert(image_pin_source_key() == "image");
+    assert(service_create_carries_image() == false);
+}
+
+test created_service_shape {
+    const cs = CreatedService { id: "s1", name: "trios-train-seed-43", project_id: "p" };
+    assert(cs.id == "s1");
+    assert(cs.name == "trios-train-seed-43");
+    assert(cs.project_id == "p");
+}