fix(landscape): accept an empty run body; pin the builder's Alpine release

POST /landscape/runs documents an optional body, but DecodeJSON returned
io.EOF on an empty one and the handler turned that into 400 — breaking the
most common call, an all-defaults run. decodeRunRequest now treats io.EOF as
the zero request; a malformed body is still 400.

The Dockerfile's Alpine ABI coupling was enforced only by a comment: a
floating golang:1.26-alpine builder against a pinned alpine:3.24 runtime
would build green and die at startup on a libgdal soname mismatch as soon as
the Go image rolls forward. Both stages are now pinned to 3.24.

Also: the route-mount test walks the router so all six routes are asserted
(GET /slots and GET /results included), and the spec documents the 404 those
two return when migration 00011's seeded groups are absent.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/transport/http/landscape_handler.go

@@ -1,6 +1,8 @@
 package http
 
 import (
+	"errors"
+	"io"
 	"net/http"
 
 	"gis/internal/landscape"
@@ -89,12 +91,26 @@ func (h *LandscapeHandler) uploadSlot(w http.ResponseWriter, r *http.Request) {
 	httputil.WriteJSON(w, http.StatusCreated, dataset)
 }
 
+// decodeRunRequest reads the run body. The whole body is optional — every field
+// has a default — so an empty body is the zero request (a default incremental
+// run), not an error. A malformed body writes a 400 and reports false.
+func decodeRunRequest(w http.ResponseWriter, r *http.Request) (runRequest, bool) {
+	req, err := httputil.DecodeJSON[runRequest](w, r)
+	switch {
+	case errors.Is(err, io.EOF):
+		return runRequest{}, true
+	case err != nil:
+		httputil.WriteError(w, http.StatusBadRequest, "invalid request body")
+		return runRequest{}, false
+	}
+	return req, true
+}
+
 // createRun queues a Landscape Program run and returns it with 202 Accepted;
 // the worker executes it asynchronously.
 func (h *LandscapeHandler) createRun(w http.ResponseWriter, r *http.Request) {
-	req, err := httputil.DecodeJSON[runRequest](w, r)
-	if err != nil {
-		httputil.WriteError(w, http.StatusBadRequest, "invalid request body")
+	req, ok := decodeRunRequest(w, r)
+	if !ok {
 		return
 	}
 	if err := h.validate.Struct(req); err != nil {

internal/transport/http/landscape_handler_test.go

@@ -3,6 +3,7 @@ package http
 import (
 	"net/http"
 	"net/http/httptest"
+	"sort"
 	"strings"
 	"testing"
 
@@ -90,31 +91,101 @@ func TestGetRunInvalidID(t *testing.T) {
 	}
 }
 
-// TestRegisterMountsRoutes checks the route table itself: every path reaches a
-// handler (405/404 would mean it is not mounted). Each request is one that is
-// rejected before the service is used.
+// TestDecodeRunRequestEmptyBody pins the "all defaults" call: POST
+// /landscape/runs with no body at all is a valid request, not a 400. Tested at
+// the helper level because the 202 path needs a live service.
+func TestDecodeRunRequestEmptyBody(t *testing.T) {
+	for _, body := range []string{"", "{}"} {
+		req := httptest.NewRequest(http.MethodPost, "/landscape/runs", strings.NewReader(body))
+		rec := httptest.NewRecorder()
+
+		got, ok := decodeRunRequest(rec, req)
+		if !ok {
+			t.Fatalf("body %q: decodeRunRequest reported failure with status %d", body, rec.Code)
+		}
+		if got.FromStage != nil || len(got.Overrides) != 0 || got.Params != nil {
+			t.Fatalf("body %q: got %+v, want the zero request", body, got)
+		}
+		if rec.Code != http.StatusOK || rec.Body.Len() != 0 {
+			t.Fatalf("body %q: helper wrote a response (status %d, body %s)", body, rec.Code, rec.Body.String())
+		}
+		// The zero request must also survive validation, or an empty body
+		// would still be rejected one step later.
+		if err := validator.New(validator.WithRequiredStructEnabled()).Struct(got); err != nil {
+			t.Fatalf("body %q: zero request fails validation: %v", body, err)
+		}
+	}
+}
+
+func TestDecodeRunRequestMalformedBody(t *testing.T) {
+	req := httptest.NewRequest(http.MethodPost, "/landscape/runs", strings.NewReader(`{`))
+	rec := httptest.NewRecorder()
+
+	if _, ok := decodeRunRequest(rec, req); ok {
+		t.Fatal("decodeRunRequest accepted a truncated body")
+	}
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+	}
+}
+
+// TestRegisterMountsRoutes walks the route table of a router with the handler
+// registered, so every one of the six routes is checked — including GET /slots
+// and GET /results, which cannot be exercised without a live service.
 func TestRegisterMountsRoutes(t *testing.T) {
 	r := chi.NewRouter()
 	r.Route("/landscape", newLandscapeTestHandler().Register)
 
-	cases := []struct {
-		method, path, body, contentType string
-		want                            int
-	}{
-		{http.MethodPost, "/landscape/runs", `{`, "application/json", http.StatusBadRequest},
-		{http.MethodPost, "/landscape/slots/lp-z-lcr", `{}`, "application/json", http.StatusBadRequest},
-		{http.MethodGet, "/landscape/runs?page=0", "", "", http.StatusBadRequest},
-		{http.MethodGet, "/landscape/runs/nope", "", "", http.StatusBadRequest},
+	got := map[string]bool{}
+	err := chi.Walk(r, func(method, route string, _ http.Handler, _ ...func(http.Handler) http.Handler) error {
+		got[method+" "+strings.TrimSuffix(route, "/")] = true
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("walk routes: %v", err)
 	}
-	for _, c := range cases {
-		req := httptest.NewRequest(c.method, c.path, strings.NewReader(c.body))
-		if c.contentType != "" {
-			req.Header.Set("Content-Type", c.contentType)
-		}
-		rec := httptest.NewRecorder()
-		r.ServeHTTP(rec, req)
-		if rec.Code != c.want {
-			t.Errorf("%s %s: status = %d, want %d (body %s)", c.method, c.path, rec.Code, c.want, rec.Body.String())
+
+	want := []string{
+		"GET /landscape/slots",
+		"POST /landscape/slots/{code}",
+		"GET /landscape/runs",
+		"POST /landscape/runs",
+		"GET /landscape/runs/{id}",
+		"GET /landscape/results",
+	}
+	for _, w := range want {
+		if !got[w] {
+			t.Errorf("route %q is not mounted; mounted routes: %v", w, keys(got))
 		}
 	}
+	if len(got) != len(want) {
+		t.Errorf("mounted %d routes, want %d: %v", len(got), len(want), keys(got))
+	}
+}
+
+// TestRoutedRequestReachesHandler sends a real request through the router so the
+// URL parameter wiring (chi.URLParam) is exercised, not just the pattern.
+func TestRoutedRequestReachesHandler(t *testing.T) {
+	r := chi.NewRouter()
+	r.Route("/landscape", newLandscapeTestHandler().Register)
+
+	req := httptest.NewRequest(http.MethodGet, "/landscape/runs/nope", nil)
+	rec := httptest.NewRecorder()
+	r.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d (body %s)", rec.Code, http.StatusBadRequest, rec.Body.String())
+	}
+	if !strings.Contains(rec.Body.String(), "invalid id") {
+		t.Fatalf("body %s does not report the bad id", rec.Body.String())
+	}
+}
+
+func keys(m map[string]bool) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
 }