Add an update_channel setting (stable|experimental) that selects which git-tag
stream the self-updater tracks on the single linear master line:
stable -> 'v*' promoted, soaked releases (default; unchanged glob)
experimental -> 'exp-v*' every release batch (opt-in testers)
A channel is only a tag glob — no branches, no divergence — so every ff-only
guarantee (#2653/#2846/#3140) is preserved. Channel governs the WebUI repo only;
the Agent repo keeps its historical branch fall-through.
Correctness (advisor-reviewed, Codex + Fable):
- describe uses --match <glob> so a commit tagged both v* and exp-v* resolves
to the channel-correct tag
- stable never falls through to origin/master when HEAD contains the latest
stable tag (the firehose-suppression that makes channels work)
- apply_force_update refuses to reset --hard onto an ancestor ref (rewind guard)
- update cache + in-progress guard keyed by (channel, include_agent)
- channel display badge is a SEPARATE field; WEBUI_VERSION stays channel-neutral
(asset cache-busting / SW cache / stale-client skew all do exact-string equality)
Settings UX: channel dropdown with risk-forward copy + the ff-only asymmetry
helper ('switching back to Stable keeps your current version until Stable catches
up'), channel chip on the version badge, i18n keys, re-check on switch.
Tests: new tests/test_update_channels.py (12 real-git-fixture tests) + existing
update suite updated for the channel-aware signatures.
2cf43527a3
