Show which model Codex sessions use (#189)

## Summary

- Codex sessions now display the model name (e.g. gpt-5-codex, o3-pro)
alongside each message, matching what Gemini sessions already show
- Makes it easy to see at a glance which model was used for each turn,
including when models change mid-session

## How it works

Codex writes a `turn_context` entry at the start of each user turn
containing the active model. The parser now reads this and stamps it on
all messages in that turn.

## Changes

- Parse `turn_context` entries from Codex JSONL and extract the `model`
field
- Track current model in the session builder and apply it to all
subsequent messages (both text and tool calls)
- Add `CodexTurnContextJSON` test helper
- Three test cases: model applied to messages, model changes across
turns, no turn_context

## Test plan

- [x] New unit tests pass (`TestParseCodexSession_TurnContextModel`)
- [x] All existing Codex parser tests pass (27 tests)
- [x] `go vet` and `go fmt` clean
- [ ] Verify with real Codex session files containing `turn_context`
entries

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: clkao

internal/parser/codex.go

@@ -15,6 +15,7 @@ import (
 const (
 	codexTypeSessionMeta  = "session_meta"
 	codexTypeResponseItem = "response_item"
+	codexTypeTurnContext  = "turn_context"
 	codexOriginatorExec   = "codex_exec"
 )
 
@@ -29,6 +30,7 @@ type codexSessionBuilder struct {
 	project      string
 	ordinal      int
 	includeExec  bool
+	currentModel string
 }
 
 func newCodexSessionBuilder(
@@ -64,6 +66,8 @@ func (b *codexSessionBuilder) processLine(
 	switch gjson.Get(line, "type").Str {
 	case codexTypeSessionMeta:
 		return b.handleSessionMeta(payload)
+	case codexTypeTurnContext:
+		b.currentModel = payload.Get("model").Str
 	case codexTypeResponseItem:
 		b.handleResponseItem(payload, ts)
 	}
@@ -125,6 +129,7 @@ func (b *codexSessionBuilder) handleResponseItem(
 		Content:       content,
 		Timestamp:     ts,
 		ContentLength: len(content),
+		Model:         b.currentModel,
 	})
 	b.ordinal++
 }
@@ -147,6 +152,7 @@ func (b *codexSessionBuilder) handleFunctionCall(
 		Timestamp:     ts,
 		HasToolUse:    true,
 		ContentLength: len(content),
+		Model:         b.currentModel,
 		ToolCalls: []ParsedToolCall{{
 			ToolName:  name,
 			Category:  NormalizeToolCategory(name),

internal/parser/codex_parser_test.go

@@ -278,6 +278,70 @@ func TestParseCodexSession_InputJSON(t *testing.T) {
 	})
 }
 
+func TestParseCodexSession_TurnContextModel(t *testing.T) {
+	t.Run("model from turn_context applied to subsequent messages", func(t *testing.T) {
+		content := testjsonl.JoinJSONL(
+			testjsonl.CodexSessionMetaJSON("m-1", "/tmp", "user", tsEarly),
+			testjsonl.CodexTurnContextJSON("gpt-5-codex", tsEarlyS1),
+			testjsonl.CodexMsgJSON("user", "hello", tsEarlyS1),
+			testjsonl.CodexMsgJSON("assistant", "hi there", tsEarlyS5),
+		)
+		sess, msgs := runCodexParserTest(t, "test.jsonl", content, false)
+		require.NotNil(t, sess)
+		assert.Equal(t, 2, len(msgs))
+		assert.Equal(t, "gpt-5-codex", msgs[0].Model)
+		assert.Equal(t, "gpt-5-codex", msgs[1].Model)
+	})
+
+	t.Run("model changes across turns", func(t *testing.T) {
+		content := testjsonl.JoinJSONL(
+			testjsonl.CodexSessionMetaJSON("m-2", "/tmp", "user", tsEarly),
+			testjsonl.CodexTurnContextJSON("gpt-5-codex", tsEarlyS1),
+			testjsonl.CodexMsgJSON("user", "hello", tsEarlyS1),
+			testjsonl.CodexMsgJSON("assistant", "hi", tsEarlyS5),
+			testjsonl.CodexTurnContextJSON("o3-pro", tsLate),
+			testjsonl.CodexMsgJSON("user", "think harder", tsLate),
+			testjsonl.CodexMsgJSON("assistant", "deep thought", tsLateS5),
+		)
+		_, msgs := runCodexParserTest(t, "test.jsonl", content, false)
+		assert.Equal(t, 4, len(msgs))
+		assert.Equal(t, "gpt-5-codex", msgs[0].Model)
+		assert.Equal(t, "gpt-5-codex", msgs[1].Model)
+		assert.Equal(t, "o3-pro", msgs[2].Model)
+		assert.Equal(t, "o3-pro", msgs[3].Model)
+	})
+
+	t.Run("empty model in turn_context clears previous model", func(t *testing.T) {
+		content := testjsonl.JoinJSONL(
+			testjsonl.CodexSessionMetaJSON("m-4", "/tmp", "user", tsEarly),
+			testjsonl.CodexTurnContextJSON("gpt-5-codex", tsEarlyS1),
+			testjsonl.CodexMsgJSON("user", "hello", tsEarlyS1),
+			testjsonl.CodexMsgJSON("assistant", "hi", tsEarlyS5),
+			testjsonl.CodexTurnContextJSON("", tsLate),
+			testjsonl.CodexMsgJSON("user", "follow up", tsLate),
+			testjsonl.CodexMsgJSON("assistant", "reply", tsLateS5),
+		)
+		_, msgs := runCodexParserTest(t, "test.jsonl", content, false)
+		assert.Equal(t, 4, len(msgs))
+		assert.Equal(t, "gpt-5-codex", msgs[0].Model)
+		assert.Equal(t, "gpt-5-codex", msgs[1].Model)
+		assert.Empty(t, msgs[2].Model)
+		assert.Empty(t, msgs[3].Model)
+	})
+
+	t.Run("no turn_context leaves model empty", func(t *testing.T) {
+		content := testjsonl.JoinJSONL(
+			testjsonl.CodexSessionMetaJSON("m-3", "/tmp", "user", tsEarly),
+			testjsonl.CodexMsgJSON("user", "hello", tsEarlyS1),
+			testjsonl.CodexMsgJSON("assistant", "hi", tsEarlyS5),
+		)
+		_, msgs := runCodexParserTest(t, "test.jsonl", content, false)
+		assert.Equal(t, 2, len(msgs))
+		assert.Empty(t, msgs[0].Model)
+		assert.Empty(t, msgs[1].Model)
+	})
+}
+
 func TestParseCodexSession_EdgeCases(t *testing.T) {
 	t.Run("skips system messages", func(t *testing.T) {
 		content := testjsonl.JoinJSONL(

internal/testjsonl/testjsonl.go

@@ -217,6 +217,20 @@ func CodexFunctionCallFieldsJSON(
 	return mustMarshal(m)
 }
 
+// CodexTurnContextJSON returns a Codex turn_context entry as a
+// JSON string with the given model.
+func CodexTurnContextJSON(model, timestamp string) string {
+	m := map[string]any{
+		"type":      "turn_context",
+		"timestamp": timestamp,
+		"payload": map[string]any{
+			"model": model,
+			"cwd":   "/tmp",
+		},
+	}
+	return mustMarshal(m)
+}
+
 // ClaudeEntryJSON returns a Claude JSONL entry with uuid and
 // parentUuid fields.
 func ClaudeEntryJSON(