feat/batch-changes: drop unneeded v3 cache-key canonicalization

The Step.MarshalJSON canonicalization and v3 image→container parse-time
mirroring are not required for server-side codingAgent execution: the
server canonicalizes container on the wire, so src-cli receives
container-only JSON and reads step.Container directly.

These changes hardened src-cli's local handling of v3 specs (preview /
validate / apply paths) but were already broken pre-PR; restoring that is
out of scope here. Drop them to keep this PR focused on the codingAgent
feature.

Author: taras-yemets

lib/batches/batch_spec.go

@@ -1,7 +1,6 @@
 package batches
 
 import (
-	"encoding/json"
 	"fmt"
 	"strings"
 
@@ -113,23 +112,6 @@ type CodingAgentStep struct {
 	Prompt string          `json:"prompt,omitempty" yaml:"prompt"`
 }
 
-// MarshalJSON canonicalizes the v3 `image:` field into `container:` on the
-// wire. Both fields exist on Step for ergonomic reasons (v3 specs use
-// `image:`, v1/v2 specs use `container:`), but src-cli's executor reads
-// `Container`. Without canonicalization, the prep-side cache key — computed
-// by JSON-marshaling Step — would include `image` while the executor side
-// (which round-trips through src-cli) would not, producing divergent keys
-// and silent cache misses for any v3 spec.
-func (s Step) MarshalJSON() ([]byte, error) {
-	type stepAlias Step
-	canon := stepAlias(s)
-	if canon.Container == "" {
-		canon.Container = canon.Image
-	}
-	canon.Image = ""
-	return json.Marshal(canon)
-}
-
 func (s *Step) IfCondition() string {
 	switch v := s.If.(type) {
 	case bool:
@@ -192,16 +174,6 @@ func parseBatchSpec(schema string, data []byte) (*BatchSpec, error) {
 		return nil, err
 	}
 
-	if spec.Version == 3 {
-		// Mirror v3 `image:` into `container:` so in-memory consumers that
-		// read step.Container (e.g. the executor transform) keep working.
-		// JSON serialization is canonicalized separately in Step.MarshalJSON
-		// so prep-side cache hashing matches src-cli/executor serialization.
-		for i := range spec.Steps {
-			spec.Steps[i].Container = spec.Steps[i].Image
-		}
-	}
-
 	var errs error
 
 	if len(spec.Steps) != 0 && spec.ChangesetTemplate == nil {
@@ -225,8 +197,7 @@ func parseBatchSpec(schema string, data []byte) (*BatchSpec, error) {
 		if step.CodingAgent != nil && step.Run != "" {
 			errs = errors.Append(errs, NewValidationError(errors.Newf("step %d: codingAgent and run cannot be combined in the same step", i+1)))
 		}
-		if step.CodingAgent != nil && step.Container == "" {
-			// v3 image: is mirrored into Container above.
+		if step.CodingAgent != nil && step.Container == "" && step.Image == "" {
 			errs = errors.Append(errs, NewValidationError(errors.Newf("step %d: codingAgent step requires an image", i+1)))
 		}
 	}

lib/batches/batch_spec_test.go

@@ -1,7 +1,6 @@
 package batches
 
 import (
-	"encoding/json"
 	"fmt"
 	"strings"
 	"testing"
@@ -27,46 +26,6 @@ changesetTemplate:
 `, stepsYAML))
 }
 
-func TestStep_MarshalJSON_canonicalizesImageToContainer(t *testing.T) {
-	v3FromImage, err := json.Marshal(Step{Image: "alpine:3", Run: "echo hi"})
-	if err != nil {
-		t.Fatalf("marshal v3-shaped step: %v", err)
-	}
-	v1FromContainer, err := json.Marshal(Step{Container: "alpine:3", Run: "echo hi"})
-	if err != nil {
-		t.Fatalf("marshal v1-shaped step: %v", err)
-	}
-	if string(v3FromImage) != string(v1FromContainer) {
-		t.Errorf("canonical JSON differs:\n  v3 image:     %s\n  v1 container: %s", v3FromImage, v1FromContainer)
-	}
-	var out map[string]any
-	if err := json.Unmarshal(v3FromImage, &out); err != nil {
-		t.Fatalf("unmarshal: %v", err)
-	}
-	if _, ok := out["image"]; ok {
-		t.Errorf("expected no image key in canonical JSON, got %s", v3FromImage)
-	}
-	if got, _ := out["container"].(string); got != "alpine:3" {
-		t.Errorf("container: got %v want alpine:3 (full=%s)", out["container"], v3FromImage)
-	}
-}
-
-func TestParseBatchSpec_v3_imageMirroredToContainer(t *testing.T) {
-	got, err := ParseBatchSpec(v3SpecWith("  - run: echo hi\n    image: alpine:3"))
-	if err != nil {
-		t.Fatalf("ParseBatchSpec failed: %v", err)
-	}
-	if len(got.Steps) != 1 {
-		t.Fatalf("expected 1 step, got %d", len(got.Steps))
-	}
-	if got.Steps[0].Image != "alpine:3" {
-		t.Errorf("Step.Image: got %q want %q", got.Steps[0].Image, "alpine:3")
-	}
-	if got.Steps[0].Container != "alpine:3" {
-		t.Errorf("Step.Container (mirrored from image): got %q want %q", got.Steps[0].Container, "alpine:3")
-	}
-}
-
 func TestParseBatchSpec_v3_codingAgentRequiresImage(t *testing.T) {
 	_, err := ParseBatchSpec(v3SpecWith("  - codingAgent:\n      type: codex\n      prompt: do the thing"))
 	if err == nil {
@@ -95,7 +54,7 @@ func TestParseBatchSpec_v3_codingAgentStep(t *testing.T) {
 	if step.CodingAgent.Prompt != "do the thing" {
 		t.Errorf("CodingAgent.Prompt: got %q want %q", step.CodingAgent.Prompt, "do the thing")
 	}
-	if step.Container != "alpine:3" {
-		t.Errorf("Step.Container (mirrored from image): got %q want %q", step.Container, "alpine:3")
+	if step.Image != "alpine:3" {
+		t.Errorf("Step.Image: got %q want %q", step.Image, "alpine:3")
 	}
 }