diff --git a/.project/concepts/e2e-harness/_debt.md b/.project/concepts/e2e-harness/_debt.md
deleted file mode 100644
index 0803289..0000000
--- a/.project/concepts/e2e-harness/_debt.md
+++ /dev/null
@@ -1,10 +0,0 @@
-# Doc-debt — e2e-harness
-
-> Presence of a block = doc to update. Processed → delete the block; no blocks left → delete this file.
-> One block = one "big change": `why` + `files` + `verify` (leaves to review).
-
-## Raw markers (consolidate into blocks, then delete)
-- TOUCHED packages/polyfill/e2e/run.ts @2026-08-12 (session f93872b5-293a-4916-a353-181409a96d42)
-- TOUCHED packages/polyfill/e2e/polyfill-entry.ts @2026-08-12 (session f93872b5-293a-4916-a353-181409a96d42)
-- TOUCHED packages/polyfill/e2e/notebook.ts @2026-08-12 (session f93872b5-293a-4916-a353-181409a96d42)
-- TOUCHED packages/polyfill/e2e/probe-frame-check.ts @2026-08-12 (session f93872b5-293a-4916-a353-181409a96d42)
diff --git a/.project/concepts/sign-in/_debt.md b/.project/concepts/sign-in/_debt.md
deleted file mode 100644
index ef55021..0000000
--- a/.project/concepts/sign-in/_debt.md
+++ /dev/null
@@ -1,7 +0,0 @@
-# Doc-debt — sign-in
-
-> Presence of a block = doc to update. Processed → delete the block; no blocks left → delete this file.
-> One block = one "big change": `why` + `files` + `verify` (leaves to review).
-
-## Raw markers (consolidate into blocks, then delete)
-- TOUCHED packages/polyfill/src/shared-wallet/access-gate.ts @2026-08-12 (session f93872b5-293a-4916-a353-181409a96d42)
diff --git a/.project/concepts/sign-in/knowledge_how-a-user-gets-in.md b/.project/concepts/sign-in/knowledge_how-a-user-gets-in.md
index a28213f..633dc73 100644
--- a/.project/concepts/sign-in/knowledge_how-a-user-gets-in.md
+++ b/.project/concepts/sign-in/knowledge_how-a-user-gets-in.md
@@ -15,6 +15,18 @@ Then the page is handed to the broker, which opens the wallet and reloads the ap
 
 What is genuinely ours is the one thing `init()` cannot do: **put the identifier into the URL before `init()` reads it**. `init()` hands over `window.location.href`; it does not know the parameter exists.
 
+## When the `barrier` shows, and why it is not a question of identity
+
+**Top-level: always. Inside the broker iframe: never** — there the identifier arrives in the URL and the page stands aside.
+
+The discriminator is the frame, not whether an identity is known, and the difference is not ergonomic. An identity is state we can observe; whether the person still has a wallet in this browser is state we cannot — it lives in another origin's storage. A screen that decides on the identity is therefore *guessing* at the state that matters, and when it guesses "already set up" while NextGraph's side is gone, it hides the only controls that could repair the situation.
+
+What that costs is not a degraded experience but a dead end: sent to the broker without a wallet, the person lands on a static page carrying **no return path to the application**. The browser's Back button is the only way out, and it only helps if the `barrier` is there to catch them on arrival.
+
+A known identifier therefore **prefills the field; it never skips the screen**. And nothing detects whether the wallet is already there: all steps are always shown, and whoever already has one ignores them. No checkbox, no "I already have it" — knowing whether you imported a wallet into this browser is not something a person can be asked.
+
+Two facts, observed on the live sites, close the alternatives: clicking the wallet application's import control opens a file chooser **in place** — no navigation, no new tab; and our own page receives **no signal at all** when the import succeeds (no opener, no message, no storage or focus event, no reload). Detecting the return is impossible, not merely fragile.
+
 ## Why the identifier travels by URL
 
 The flow runs in **two contexts with separate storage partitions** — the top-level page and the broker iframe — because browsers partition storage by top-level site. A value written top-level is not the value the iframe reads.