diff --git a/internal/transcript/codex.go b/internal/transcript/codex.go
index 528b1b3..18670fb 100644
--- a/internal/transcript/codex.go
+++ b/internal/transcript/codex.go
@@ -32,11 +32,65 @@ func isCodexUserPrompt(e map[string]any) bool {
 	case "event_msg":
 		return getStr(p, "type") == "user_message" && pyStrip(getStr(p, "message")) != ""
 	case "response_item":
-		return getStr(p, "type") == "message" && getStr(p, "role") == "user"
+		if getStr(p, "type") != "message" || getStr(p, "role") != "user" {
+			return false
+		}
+		// Text that is nothing but Codex's own injected context is not a
+		// prompt; an image-only message (no text at all) still is.
+		if text := codexUserText(p); text != "" && stripCodexInjected(text) == "" {
+			return false
+		}
+		return true
 	}
 	return false
 }
 
+// codexUserText joins the text parts of a role=user response_item payload,
+// whichever shape Codex used for content (a string or a list of parts).
+func codexUserText(p map[string]any) string {
+	switch c := p["content"].(type) {
+	case string:
+		return c
+	case []any:
+		var b strings.Builder
+		for _, x := range c {
+			bm, ok := x.(map[string]any)
+			if !ok {
+				continue
+			}
+			switch getStr(bm, "type") {
+			case "input_text", "text", "output_text":
+				b.WriteString(getStr(bm, "text"))
+			}
+		}
+		return b.String()
+	}
+	return ""
+}
+
+// Codex opens a thread, and re-opens it after a cwd change, by injecting its
+// own context as role=user response_items: the AGENTS.md chain wrapped in
+// <INSTRUCTIONS> (older builds: <user_instructions>), usually with an
+// <environment_context> block of cwd/shell/date/permissions appended, and a
+// bare <environment_context> later on. Nobody typed those. Captured as
+// prompts they open every Codex log with a ~10 KB copy of AGENTS.md, which a
+// brain fold then reads as owner instructions and re-learns in every
+// project. Anchored at the start of the text and closed by the end tag, so a
+// prompt that merely mentions a tag, or an unclosed block, is left alone.
+var codexInjectedRe = regexp.MustCompile(`(?s)\A\s*(?:# AGENTS\.md instructions.*?</INSTRUCTIONS>|<user_instructions>.*?</user_instructions>|<environment_context>.*?</environment_context>)\s*`)
+
+// stripCodexInjected removes every leading injected block from a user
+// message's text. A message that is only injected context strips to "".
+func stripCodexInjected(text string) string {
+	for {
+		loc := codexInjectedRe.FindStringIndex(text)
+		if loc == nil || loc[1] == 0 {
+			return text
+		}
+		text = text[loc[1]:]
+	}
+}
+
 // codexPromptText is _codex_prompt_text: the stripped user prompt carried by
 // an event, or "".
 func codexPromptText(e map[string]any) string {
@@ -50,23 +104,7 @@ func codexPromptText(e map[string]any) string {
 		if getStr(p, "type") != "message" || getStr(p, "role") != "user" {
 			return ""
 		}
-		switch c := p["content"].(type) {
-		case string:
-			return pyStrip(c)
-		case []any:
-			var b strings.Builder
-			for _, x := range c {
-				bm, ok := x.(map[string]any)
-				if !ok {
-					continue
-				}
-				switch getStr(bm, "type") {
-				case "input_text", "text", "output_text":
-					b.WriteString(getStr(bm, "text"))
-				}
-			}
-			return pyStrip(b.String())
-		}
+		return pyStrip(stripCodexInjected(codexUserText(p)))
 	}
 	return ""
 }
diff --git a/internal/transcript/codex_injected_test.go b/internal/transcript/codex_injected_test.go
new file mode 100644
index 0000000..14d4d9f
--- /dev/null
+++ b/internal/transcript/codex_injected_test.go
@@ -0,0 +1,65 @@
+package transcript
+
+// Codex opens a thread by injecting its own context as role=user
+// response_items: the AGENTS.md chain wrapped in <INSTRUCTIONS> (with an
+// <environment_context> block appended) and, after a cwd change, a bare
+// <environment_context>. Nobody typed those. Captured as prompts they open
+// every Codex log with a ~10 KB copy of AGENTS.md, which a brain fold then
+// reads as owner instructions and re-learns in every project.
+
+import (
+	"strings"
+	"testing"
+)
+
+const codexInjected = `{"type":"session_meta","payload":{"cwd":"/codex/inj"}}
+{"type":"turn_context","payload":{"collaboration_mode":{"settings":{"model":"gpt-5.3"}}}}
+{"type":"response_item","timestamp":"2026-08-01T00:00:00Z","payload":{"type":"message","role":"user","content":[{"type":"input_text","text":"# AGENTS.md instructions for /codex/inj\n\n<INSTRUCTIONS>\n## House rules\n\n- Never push to main.\n</INSTRUCTIONS>\n<environment_context>\n  <cwd>/codex/inj</cwd>\n  <shell>zsh</shell>\n</environment_context>"}]}}
+{"type":"response_item","timestamp":"2026-08-01T00:00:01Z","payload":{"type":"message","role":"user","content":[{"type":"input_text","text":"fix the flaky test"}]}}
+{"type":"response_item","timestamp":"2026-08-01T00:00:05Z","payload":{"type":"message","role":"assistant","content":[{"type":"output_text","text":"Pinned the clock."}]}}
+{"type":"event_msg","timestamp":"2026-08-01T00:00:06Z","payload":{"type":"token_count","info":{"last_token_usage":{"input_tokens":10,"cached_input_tokens":0,"output_tokens":5}}}}
+{"type":"response_item","timestamp":"2026-08-01T00:01:00Z","payload":{"type":"message","role":"user","content":[{"type":"input_text","text":"<environment_context>\n  <cwd>/codex/inj/sub</cwd>\n</environment_context>"}]}}
+{"type":"response_item","timestamp":"2026-08-01T00:01:01Z","payload":{"type":"message","role":"user","content":"second task"}}
+{"type":"response_item","timestamp":"2026-08-01T00:01:05Z","payload":{"type":"message","role":"assistant","content":[{"type":"output_text","text":"Done."}]}}
+{"type":"event_msg","timestamp":"2026-08-01T00:01:06Z","payload":{"type":"token_count","info":{"last_token_usage":{"input_tokens":20,"cached_input_tokens":0,"output_tokens":3}}}}
+`
+
+func TestCodexInjectedContextIsNotAPrompt(t *testing.T) {
+	t.Parallel()
+	path := writeFixture(t, "codex-injected.jsonl", codexInjected)
+	want := []string{
+		`dt=2026-08-01T00:00:01Z|cwd=/codex/inj|prompt="fix the flaky test"|texts=["Pinned the clock."]|tools=|files=|turn_ts=2026-08-01T00:00:06Z|tok=10/5/0/0|model=gpt-5.3`,
+		`dt=2026-08-01T00:01:01Z|cwd=/codex/inj|prompt="second task"|texts=["Done."]|tools=|files=|turn_ts=2026-08-01T00:01:06Z|tok=20/3/0/0|model=gpt-5.3`,
+	}
+	// Injected context is never a prompt, whichever way synthetic prompts
+	// (the <skill> markers) are treated.
+	checkTurns(t, Turns(path, 0, true), want)
+	checkTurns(t, Turns(path, 0, false), want)
+	for _, turn := range Turns(path, 0, false) {
+		if strings.Contains(turn.Prompt, "AGENTS.md") || strings.Contains(turn.Prompt, "environment_context") {
+			t.Errorf("Codex-injected context leaked into a prompt: %q", turn.Prompt)
+		}
+	}
+}
+
+func TestStripCodexInjected(t *testing.T) {
+	t.Parallel()
+	cases := []struct{ name, in, want string }{
+		{"instructions-only", "# AGENTS.md instructions for /x\n\n<INSTRUCTIONS>\n- rule\n</INSTRUCTIONS>", ""},
+		{"instructions-then-environment", "# AGENTS.md instructions\n\n<INSTRUCTIONS>\n- rule\n</INSTRUCTIONS>\n<environment_context>\n  <cwd>/x</cwd>\n</environment_context>", ""},
+		{"environment-only", "<environment_context>\n  <cwd>/x</cwd>\n</environment_context>", ""},
+		{"legacy-user-instructions", "<user_instructions>\nbe terse\n</user_instructions>", ""},
+		{"environment-then-typed-text", "<environment_context>\n  <cwd>/x</cwd>\n</environment_context>\n\nfix the flaky test", "fix the flaky test"},
+		{"typed-text-untouched", "fix the flaky test", "fix the flaky test"},
+		{"prose-mention-untouched", "why does <environment_context> appear in my logs?", "why does <environment_context> appear in my logs?"},
+		{"unclosed-block-untouched", "<environment_context>\n  <cwd>/x</cwd>", "<environment_context>\n  <cwd>/x</cwd>"},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			t.Parallel()
+			if got := stripCodexInjected(c.in); got != c.want {
+				t.Errorf("stripCodexInjected(%q) = %q, want %q", c.in, got, c.want)
+			}
+		})
+	}
+}