diff --git a/scripts/make-detection-fixture.py b/scripts/make-detection-fixture.py
index 2200cfa0..8b439960 100755
--- a/scripts/make-detection-fixture.py
+++ b/scripts/make-detection-fixture.py
@@ -3,8 +3,15 @@
 
 Implements steps 3, 6, and 7 of the capture-and-promotion procedure in
 `supacodeTests/Fixtures/AgentScreenDetection/README.md`: it rejects a capture
-that is not detector-faithful, reduces the screen to the same tail the detector
-reads, and applies redactions without changing the visible width of any line.
+that is not detector-faithful, reduces the screen to the exact slice the
+detector reads for the given agent, and applies redactions without changing
+the visible width of any line.
+
+The reduction mirrors `DetectedAgent.detectionScreenText(from:)`: `claude`
+consumes the full active screen and is passed through untrimmed, while every
+other agent consumes the bounded 24-line tail. `--agent` selects between the
+two, and is required because the capture does not record which detector will
+consume it.
 
 Width matters. A fixture exists to pin how the classifier reads a real screen,
 and the agent CLIs wrap, shorten, and truncate their rows to the terminal width.
@@ -15,6 +22,7 @@ either preserves the line's visible width or is refused.
 Usage:
 
     scripts/make-detection-fixture.py capture.json \\
+        --agent claude \\
         --redact /Users/me=/Users/usr \\
         --redact 'Acme Inc=<ORG_0000>' \\
         > supacodeTests/Fixtures/AgentScreenDetection/claude/2.1.226/idle/composer.txt
@@ -63,6 +71,16 @@ def canonical_tail(content: str, limit: int = DETECTOR_TAIL_LIMIT) -> str:
     return "\n".join(lines[start:])
 
 
+def detection_screen_text(text: str, agent: str) -> str:
+    """Port of `DetectedAgent.detectionScreenText(from:)`.
+
+    `claude` consumes the full active screen; every other agent consumes the
+    bounded tail. The special case is deliberate on the Swift side: trimming a
+    Claude capture can delete the very row that reproduces a bug.
+    """
+    return text if agent == "claude" else canonical_tail(text)
+
+
 class FixtureError(Exception):
     """A capture could not be turned into a faithful fixture."""
 
@@ -213,6 +231,14 @@ def main() -> int:
     parser.add_argument(
         "capture", help="JSON emitted by `prowl read --source detection --json`"
     )
+    parser.add_argument(
+        "--agent",
+        required=True,
+        metavar="AGENT",
+        help="detector the fixture targets (the <runtime> path component, e.g. claude "
+        "or codex); claude keeps the full screen, every other agent takes the "
+        "bounded 24-line tail",
+    )
     parser.add_argument(
         "--redact",
         action="append",
@@ -247,7 +273,8 @@ def main() -> int:
     # text back into the repository the redaction was protecting.
     applied: dict[str, int] = {}
     out_lines = []
-    for number, line in enumerate(canonical_tail(data["text"]).split("\n"), start=1):
+    reduced = detection_screen_text(data["text"], args.agent)
+    for number, line in enumerate(reduced.split("\n"), start=1):
         for old, new in args.redact:
             try:
                 replaced = substitute(line, old, new)
diff --git a/scripts/test_make_detection_fixture.py b/scripts/test_make_detection_fixture.py
index ab2f8a62..90875f89 100644
--- a/scripts/test_make_detection_fixture.py
+++ b/scripts/test_make_detection_fixture.py
@@ -116,14 +116,38 @@ class MoneyMasking(unittest.TestCase):
         self.assertEqual(len(applied), 2)
 
 
+class Reduction(unittest.TestCase):
+    def test_claude_keeps_the_full_screen(self):
+        # Mirrors `DetectedAgent.detectionScreenText(from:)`: trimming a Claude
+        # capture can delete the very row that reproduces a bug.
+        text = "\n".join(f"line {index}" for index in range(40))
+        self.assertEqual(fixture.detection_screen_text(text, "claude"), text)
+
+    def test_other_agents_take_the_bounded_tail(self):
+        text = "\n".join(f"line {index}" for index in range(40))
+        reduced = fixture.detection_screen_text(text, "codex")
+        self.assertEqual(reduced.split("\n"), [f"line {index}" for index in range(16, 40)])
+
+    def test_blank_lines_do_not_count_toward_the_tail_budget(self):
+        rows = [f"line {index}" for index in range(30)]
+        rows.insert(28, "")
+        reduced = fixture.detection_screen_text("\n".join(rows), "codex")
+        self.assertEqual(len(reduced.split("\n")), 25)
+        self.assertIn("", reduced.split("\n"))
+
+    def test_short_screens_pass_through_for_every_agent(self):
+        text = "a\n\nb"
+        self.assertEqual(fixture.detection_screen_text(text, "codex"), text)
+
+
 class EndToEnd(unittest.TestCase):
-    def run_script(self, text, *args):
+    def run_script(self, text, *args, agent="claude"):
         with tempfile.NamedTemporaryFile("w", suffix=".json", delete=False) as handle:
             json.dump({"data": {"source": "detection", "text": text}}, handle)
             path = handle.name
         try:
             return subprocess.run(
-                [sys.executable, str(SCRIPT), path, *args],
+                [sys.executable, str(SCRIPT), path, "--agent", agent, *args],
                 capture_output=True,
                 text=True,
             )
@@ -156,13 +180,24 @@ class EndToEnd(unittest.TestCase):
         self.assertEqual(result.returncode, 1)
         self.assertIn("no width terminals agree on", result.stderr)
 
+    def test_agent_selects_the_reduction(self):
+        text = "\n".join(f"row {index}" for index in range(30))
+        full = self.run_script(text)
+        tail = self.run_script(text, agent="codex")
+        self.assertEqual(full.stdout, text)
+        self.assertEqual(tail.stdout, "\n".join(f"row {index}" for index in range(6, 30)))
+
     def test_viewport_capture_is_still_rejected(self):
         with tempfile.NamedTemporaryFile("w", suffix=".json", delete=False) as handle:
             json.dump({"data": {"source": "screen", "text": "x"}}, handle)
             path = handle.name
         try:
+            # `--agent` is passed so exit 2 comes from the source check, not
+            # from argparse rejecting a missing required flag with the same code.
             result = subprocess.run(
-                [sys.executable, str(SCRIPT), path], capture_output=True, text=True
+                [sys.executable, str(SCRIPT), path, "--agent", "claude"],
+                capture_output=True,
+                text=True,
             )
         finally:
             pathlib.Path(path).unlink()
diff --git a/supacodeTests/Fixtures/AgentScreenDetection/README.md b/supacodeTests/Fixtures/AgentScreenDetection/README.md
index b13d2389..311c4fe4 100644
--- a/supacodeTests/Fixtures/AgentScreenDetection/README.md
+++ b/supacodeTests/Fixtures/AgentScreenDetection/README.md
@@ -56,11 +56,17 @@ steps and refuses a substitution it cannot fit:
 
 ```bash
 scripts/make-detection-fixture.py .local/agent-screen-captures/capture.json \
+  --agent claude \
   --redact "/Users/me=/Users/usr" \
   --redact "Acme Inc=<ORG_0000>" \
   > claude/2.1.226/idle/composer.txt
 ```
 
+`--agent` is required and selects the step 6 reduction: `claude` keeps the full active
+screen, and every other agent value takes the bounded 24-line tail. The flag mirrors
+`DetectedAgent.detectionScreenText(from:)` rather than reading the agent from the
+capture, because the capture does not record which detector will consume it.
+
 Each replacement is padded or trimmed in the spaces immediately following it, so every
 later column on the row — a closing box border, a second column of chrome — keeps its
 captured position. A replacement too long for the space after it fails with the maximum