Address seed-packet review: 413 mapping, deadline, rollback, dedup

Gadfly findings on #94, the real ones:

- scanSeedPacket extends only the READ deadline; a slow upload + a live
  vision call runs past the server's absolute 30s WriteTimeout and the
  successful response is silently dropped (the #78 failure mode). Extend
  the write deadline too (scanWriteTimeout).
- An oversized upload tripping MaxBytesReader was mapped to 400; it's 413.
  Detect *http.MaxBytesError and report IMAGE_TOO_LARGE.
- Split imagenorm error mapping: ErrTooLarge->413, ErrUnsupported->400,
  genuine read/encode faults (and a failed file.Open)->500, not 400.
- CreateFromPacket discarded the plant it created when the lot then
  failed, contradicting its own doc. Roll the new plant back instead so
  the confirm is all-or-nothing (a fresh plant has no lots/plantings, so
  the delete is safe; log-and-continue on cleanup failure).
- Dedup: packetLotRequest and seedLotCreateRequest shared every lot
  field. Extract a seedLotFields base both use. validCategory now reuses
  plantCategories. EffectiveConfig resolves agent+vision from one
  settings-row read instead of two.
- capabilities swallowed an EffectiveVision error silently; log it.
- vision test hand-copied Extract's body (drift risk). Split generate()
  out of Extract so the hermetic test drives the real request builder.

Tests: rollback-on-lot-failure (service), oversized->413 (api).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

internal/vision/vision_test.go

@@ -24,18 +24,6 @@ func tinyJPEG(t *testing.T) []byte {
 	return b.Bytes()
 }
 
-// extractVia is Extract with a caller-supplied registry, so the test can point it
-// at a fake provider instead of resolving a live model. It mirrors Extract's body
-// exactly apart from where the model comes from.
-func extractVia(t *testing.T, m llm.Model, jpeg []byte) (SeedPacket, error) {
-	t.Helper()
-	return majordomo.Generate[SeedPacket](context.Background(), m, majordomo.Request{
-		Messages: []majordomo.Message{
-			majordomo.UserParts(majordomo.Text(extractPrompt), majordomo.Image("image/jpeg", jpeg)),
-		},
-	})
-}
-
 // TestExtractParsesModelJSON is the hermetic proof that the extraction path works
 // end to end without a live model: a fake vision model returns canned packet JSON
 // and Generate[SeedPacket] unmarshals it into the struct, image and schema
@@ -62,7 +50,7 @@ func TestExtractParsesModelJSON(t *testing.T) {
 		t.Fatalf("parse: %v", err)
 	}
 
-	got, err := extractVia(t, m, tinyJPEG(t))
+	got, err := generate(context.Background(), m, tinyJPEG(t))
 	if err != nil {
 		t.Fatalf("extract: %v", err)
 	}
@@ -102,7 +90,7 @@ func TestExtractLeavesMissingFieldsNil(t *testing.T) {
 	fp.Enqueue("vision", fake.Reply(`{"species":"basil","category":"herb"}`))
 	m, _ := reg.Parse("fp/vision")
 
-	got, err := extractVia(t, m, tinyJPEG(t))
+	got, err := generate(context.Background(), m, tinyJPEG(t))
 	if err != nil {
 		t.Fatalf("extract: %v", err)
 	}