docs: retire mv2 branch guidance

AGENTS.md

@@ -3,7 +3,7 @@
 ## Branch Discipline
 
 - `main` is the only maintained source branch. Make code changes there.
-- `mv3` and `mv3-ltl` are retired. The remote `mv2` branch is a temporary rollback reference until LiveTL migration and runtime validation finish; do not use it for new work or delete it early.
+- `mv3`, `mv3-ltl`, and `mv2` are retired. Do not use them for new work.
 - There is no branch ladder any more. MV2 and MV3 are **build targets on `main`**, not branches — see "Manifest Version Targets" below.
 - If a task touches both HyperChat and LiveTL, HyperChat still goes first.
 - Cross-repo order is mandatory:
@@ -29,7 +29,7 @@
 ## Manifest Version Targets
 
 - `main` builds three targets: `chrome` (MV3), `firefox` (MV3), and `mv2` (MV2, Firefox-only).
-- The `mv2` target is **not** legacy cruft. Firefox's MV3 support is unreliable for LiveTL's needs, so LiveTL's Firefox variant will consume it after the downstream migration. Do not "simplify" it away.
+- The `mv2` target is **not** legacy cruft. Firefox's MV3 support is unreliable for LiveTL's needs, so LiveTL's Firefox variant consumes it. Do not "simplify" it away.
 - Keep the MV2/MV3 distinction in exactly two places:
   - `src/manifest.json` — `{{mv2}}.` / `{{mv3}}.` key prefixes, resolved by `scripts/resolve-manifest.ts`. The MV tag must come **first** in nested keys (`{{mv3}}.{{firefox}}.background`); the reverse order leaks a literal tag into the built manifest.
   - `__MV__` in source — a build-time constant, so unused branches are dropped per target.

README.md

@@ -21,8 +21,8 @@ See https://livetl.app/hyperchat/install
 
 Everything ships from `main`. There is one source tree and three build targets:
 
-> Transition status: migrating both LiveTL lines to this source and deleting the
-> remote `mv2` rollback branch are still pending runtime validation.
+Use `main`; do not check out the historical `mv2` branch. `mv2` below names a
+build target.
 
 | Target    | Manifest          | Consumer                                                                               |
 | --------- | ----------------- | -------------------------------------------------------------------------------------- |

RELEASE_PROCESS.md

@@ -3,9 +3,8 @@
 Everything ships from `main`. There is no branch ladder — MV2 and MV3 are build
 targets, not branches.
 
-`mv3` and `mv3-ltl` are historical. The remote `mv2` branch is rollback-only
-until LiveTL migration and runtime validation finish; do not route maintenance
-through it or delete it early.
+`mv3`, `mv3-ltl`, and `mv2` are historical branches. Do not route maintenance
+through them; `mv2` below names the build target on `main`.
 
 ## Branch Order
 
@@ -76,5 +75,5 @@ for b in ['HyperChat-chrome.zip','HyperChat-firefox.zip']:
 ## Notes For LiveTL Sync
 
 LiveTL consumes HyperChat via git submodules, not release assets. Its MV2 Firefox
-variant and MV3 line will both track `main` after the downstream migration. Until
-their release pins and runtime checks pass, keep the remote `mv2` rollback branch.
+variant and MV3 line both track HyperChat `main`; never repoint either to the
+historical `mv2` branch.