docs: describe all tag-door assertions

README.md

@@ -146,13 +146,15 @@ refusal is the single failure in this file that leaves a real release behind.
 
 - **The tag door — the fallback and the backfill.** A bare `X.Y.Z` tag push
   — **no `v` prefix**, box's 0.6.0 set the scheme
-  ([release.yml](.github/workflows/release.yml#L303-L371)) — publishes the
+  ([release.yml](.github/workflows/release.yml#L316-L401)) — publishes the
   same way. The tag is the operator's explicit act, so there is no decide
-  and no label check — what is left is two asserts: **the tag names the
+  and no label check — what is left is three asserts: **the tag names the
   tree's own version**
-  ([L328–L339](.github/workflows/release.yml#L328-L339)) and **the tagged
+  ([L341–L352](.github/workflows/release.yml#L341-L352)), **the tagged
   tree carries a publishable `## X.Y.Z` section**
-  ([L340–L352](.github/workflows/release.yml#L340-L352)); either failing
+  ([L353–L365](.github/workflows/release.yml#L353-L365)), and **no published
+  release already exists for the tag**
+  ([L366–L381](.github/workflows/release.yml#L366-L381)); any failure
   refuses, creating nothing. No `-dev` bump either
   — the fallback does not rewrite main (cast's precedent). Use it when the
   merge path is red, for backfills, and for the
@@ -503,25 +505,31 @@ release and the
 [armed guard's window](#changelog-armed--main-never-sits-disarmed) stays
 open.
 
-### The tag door refused ([release.yml](.github/workflows/release.yml#L303-L371))
+### The tag door refused ([release.yml](.github/workflows/release.yml#L316-L401))
 
 > tag '$GITHUB_REF_NAME' does not match the tree's version '$ver' — creating nothing.
 > A release is a PR, then a tag: the release PR bumps the version and stamps the changelog; the tag goes on its MERGE commit. Delete this tag and re-tag the right commit.
 
-[L333–L337](.github/workflows/release.yml#L333-L337). The message is the
+[L347–L350](.github/workflows/release.yml#L347-L350). The message is the
 remedy.
 
 > CHANGELOG.md has no '## $VER' section — run changelog-assemble in the release PR before tagging; refusing to publish an empty release
 
-[L346–L349](.github/workflows/release.yml#L346-L349). The tagged tree was
+[L359–L365](.github/workflows/release.yml#L359-L365). The tagged tree was
 never stamped. Assemble the section
 ([docs/CONSUMERS.md](docs/CONSUMERS.md#assembling-a-release-section)), then
 delete and re-push the tag.
 
+> release '$VER' already exists — refusing to re-release, creating nothing.
+
+[L366–L381](.github/workflows/release.yml#L366-L381). A published release is
+never replaced by the fallback. If it is correct, there is nothing to do; if
+it is wrong, correct that published artifact deliberately before retrying.
+
 ### The re-arm refused ([release.yml](.github/workflows/release.yml#L267-L301))
 
 The bump belongs to the merge door alone — the tag door deliberately does not
-rewrite main ([L303–L307](.github/workflows/release.yml#L303-L307)) — and it
+rewrite main ([L316–L320](.github/workflows/release.yml#L316-L320)) — and it
 runs *after* the tag, the notes and the publish. So a refusal here leaves a
 real release standing behind a main that never re-armed — the release exists,
 and main is left *armed to impersonate* it, still reading the version it just