diff --git a/backend/apps/agents/browser/browser_send_parse.py b/backend/apps/agents/browser/browser_send_parse.py
index 723dbba5..df114d56 100644
--- a/backend/apps/agents/browser/browser_send_parse.py
+++ b/backend/apps/agents/browser/browser_send_parse.py
@@ -38,9 +38,13 @@ P_LOGIN_WALL_URL_RE = re.compile(
     r"/(?:log[_-]?in|sign[_-]?in|signin|logon)(?:[/?#]|$)",
     re.I,
 )
+# A password box disqualifies the page whoever is signed in: whatever that form is for, typing a
+# post into it is wrong. Kept apart from the softer copy below because only this one is absolute.
+P_PASSWORD_FIELD_RE = re.compile(r'<\s*textbox\s+"[^"]*(?:password|passwd)', re.I)
+# Wording a login screen uses. Also, unfortunately, wording a signed-IN page uses in its footer and
+# its upsells, which is why this half is overridable and the password field is not.
 P_LOGIN_WALL_STATE_RE = re.compile(
-    r'<\s*textbox\s+"[^"]*(?:password|passwd)|(?:log|sign)\s?in to |'
-    r"continue with (?:google|apple|facebook)",
+    r"(?:log|sign)\s?in to |continue with (?:google|apple|facebook)",
     re.I,
 )
 
@@ -64,13 +68,37 @@ P_READONLY_RE = re.compile(
 )
 
 
+def login_wall_reason(current_url: str, state_text: str) -> str:
+    """WHY this page reads as a login wall, or "" when it does not.
+
+    The bool alone sent a whole site to the model path with nothing to debug against: substack
+    declined as a wall on `https://substack.com/` while the account was demonstrably signed in, and
+    no amount of staring at the regexes reproduced it. A gate that can silently cost a site its
+    entire write path should be able to say which words convinced it."""
+    if current_url and P_LOGIN_WALL_URL_RE.search(current_url):
+        return f"url: {P_LOGIN_WALL_URL_RE.search(current_url).group(0)}"
+    if not state_text:
+        return ""
+    pw = P_PASSWORD_FIELD_RE.search(state_text)
+    if pw:
+        return f"password field: {pw.group(0)[:60]}"
+    soft = P_LOGIN_WALL_STATE_RE.search(state_text)
+    if not soft:
+        return ""
+    # "Sign in to ..." and "Continue with Google" are what a login screen says, and ALSO what a
+    # signed-in page's footer, upsell and embedded-content strip say. Treating them as proof cost
+    # substack its whole write path. The veto looks_signed_out already trusts settles it: a control
+    # that is meaningless unless you are authenticated outranks marketing copy.
+    if P_SIGNED_IN_RE.search(state_text):
+        return ""
+    return f"copy: {soft.group(0)[:60]}"
+
+
 def looks_like_login_wall(current_url: str, state_text: str) -> bool:
     """A login/auth page (by URL) or an auth form in the perception (a password field, a
     'Log in to X' heading, an OAuth 'Continue with ...'). The scripted send declines here:
     a real composer never shares a page with these, and filling here types a login field."""
-    if current_url and P_LOGIN_WALL_URL_RE.search(current_url):
-        return True
-    return bool(state_text and P_LOGIN_WALL_STATE_RE.search(state_text))
+    return bool(login_wall_reason(current_url, state_text))
 
 
 # SOFT signed-out: the site serves a browsable page with no auth form and no login URL, it just
diff --git a/backend/tests/test_browser_login_wall.py b/backend/tests/test_browser_login_wall.py
new file mode 100644
index 00000000..5e81d03b
--- /dev/null
+++ b/backend/tests/test_browser_login_wall.py
@@ -0,0 +1,49 @@
+"""The login-wall gate: what it must catch, and what it must stop catching.
+
+This gate exists because the reveal finder once filled an Instagram login form and armed the page's
+own submit as a "send". It is load-bearing and it fails safe, so the temptation is to leave it broad.
+
+Broad turned out to have its own cost. Measured live 2026-07-31, substack.com declined as an auth
+wall while the account was demonstrably signed in, which takes an entire site out of the write path
+for as long as nobody notices. Sites print "Sign in to ..." in footers, upsells and embedded content
+strips, and that copy is not evidence of a wall on a page that is also showing you your own account
+menu. So the copy half is overridable by a signed-in affordance and the password half is not.
+"""
+
+from backend.apps.agents.browser import browser_send_parse as sp
+
+SIGNED_IN = ('[1]<button "Account menu">\n'
+             '[4]<link "Sign in to read more">\n'
+             '[7]<textbox "Write a note">')
+
+
+def test_a_signed_in_page_is_not_a_wall_just_because_it_says_sign_in():
+    """The substack shape: login copy sitting next to proof you are already logged in."""
+    assert not sp.looks_like_login_wall("https://substack.com/", SIGNED_IN)
+
+
+def test_a_password_box_convicts_no_matter_who_is_signed_in():
+    """The veto is COPY-only on purpose. Whatever a password form is for, a post does not go in it,
+    and 'but the user is logged in' is not a reason to start typing into one."""
+    assert sp.looks_like_login_wall(
+        "https://site.com/x", '[1]<button "Sign out">\n[3]<textbox "Password">')
+
+
+def test_login_copy_still_convicts_with_nothing_to_weigh_against_it():
+    """Without a signed-in affordance the copy is the only evidence there is, and it stands."""
+    assert sp.looks_like_login_wall("https://site.com/x", '[4]<link "Log in to X to continue">')
+
+
+def test_login_urls_are_still_walls_outright():
+    """Unchanged, and not overridable: a login URL is the page's own declaration of what it is."""
+    assert sp.looks_like_login_wall("https://x.com/i/flow/login", SIGNED_IN)
+    assert sp.looks_like_login_wall("https://accounts.google.com/v3/signin/identifier", SIGNED_IN)
+
+
+def test_the_decline_names_its_own_trigger():
+    """The bool alone left a whole site declining with nothing to debug against: no amount of
+    re-reading the regexes reproduced substack, because the reason was never written down."""
+    assert "url:" in sp.login_wall_reason("https://x.com/i/flow/login", "")
+    assert "password field:" in sp.login_wall_reason("https://site.com/x", '[3]<textbox "Password">')
+    assert "copy:" in sp.login_wall_reason("https://site.com/x", "Log in to X to continue")
+    assert sp.login_wall_reason("https://substack.com/", SIGNED_IN) == ""