release: v0.50.246

Combines:
- 4 contributor PRs (#1335 user fenced code, #1337 mermaid+cache-bust,
  #1339 fallback_providers list, #1341 context_length persistence)
- Self-built #1338 (cancel data-loss + activity panel) — already
  independently APPROVED by nesquena before absorption
- CONTRIBUTORS.md and markdown refresh from #1340

See CHANGELOG.md for the full list with author credit.

CHANGELOG.md

@@ -2,6 +2,26 @@
 
 ## [Unreleased]
 
+## [v0.50.246] — 2026-04-30
+
+### Added
+- **Render fenced code blocks in user messages** — typing a triple-backtick fenced code block in the composer now renders with proper code styling, syntax-aware diff/patch coloring, and the same `<pre><code>` pipeline used for assistant responses. Plain user text outside fences stays escaped (no markdown bold/italic/links interpreted in user bubbles); only fenced blocks are upgraded. Includes specialized colored-line rendering for `diff` / `patch` languages. (`static/ui.js`, `tests/test_1325_user_fenced_code.py`) @bergeouss — PR #1335, fixes #1325
+
+### Fixed
+- **Stop/Cancel during streaming no longer wipes the user's typed message (data-loss bug)** — When a user clicked Stop while the agent was streaming, `cancel_stream()` cleared `pending_user_message` before the streaming thread had merged the user turn into `s.messages`, persisting a session with neither the pending field nor a corresponding message. The user's typed text was permanently lost from the session JSON, not just the in-memory client copy. Now `cancel_stream()` synthesizes a user turn into `s.messages` from `pending_user_message` (with attachments preserved) when the most recent user message isn't already that turn — guards against double-append by content-matching against the last user message. (`api/streaming.py`, `tests/test_issue1298_cancel_and_activity.py`) — fixes #1298 (issue 2)
+- **Activity panel no longer auto-collapses when new tool/thinking events arrive** — Both `ensureActivityGroup()` (which re-creates the group with `tool-call-group-collapsed` on every destroy/recreate) and `finalizeThinkingCard()` (which force-adds the collapsed class on every tool boundary) ignored the user's manual expand. Tracks the user's last explicit toggle on the live activity group in a per-turn singleton (`_liveActivityUserExpanded`), restored on re-create and respected by the finalize path. Cleared between turns by `clearLiveToolCards()`. (`static/ui.js`, `tests/test_issue1298_cancel_and_activity.py`) — fixes #1298 (issue 1)
+- **Stale Mermaid render errors no longer leak into every chat** — Mermaid's render-failure path leaves a temporary `<div id="d<id>">` body-level node containing a "Syntax error in text" SVG. The previous code never removed it, so once any Mermaid block failed (or got mis-detected as Mermaid), every subsequent tab kept the syntax-error SVG visible regardless of content. Also tightens Mermaid detection so line-numbered tool output (`123|line`) and code blocks that don't start with a recognized Mermaid keyword are no longer mis-parsed as Mermaid; failed blocks are marked so a later render pass can't retry them. (`static/ui.js`, `tests/test_issue347.py`) @dso2ng — PR #1337
+- **Static asset cache busts automatically on every release** — `<script src="static/ui.js">` and friends were cached indefinitely by browsers and the service worker, so a new release with bug fixes could be invisible to a user until they hard-refreshed. Now `index.html` and `sw.js` registration both inject the current `WEBUI_VERSION` git tag as a `?v=` query string, URL-encoded server-side so unusual git tag formats can't break the JS. The service worker also no longer intercepts requests for itself, ensuring the browser always fetches the freshly-versioned `sw.js` directly from the network. (`api/routes.py`, `static/index.html`, `static/sw.js`, `tests/test_pwa_manifest_sw.py`) @dso2ng — PR #1337
+- **Context window indicator persists across page reloads** — `Session.__init__` now accepts `context_length`, `threshold_tokens`, and `last_prompt_tokens`; `save()` persists them and `compact()` exposes them so the GET `/api/session` response includes them. The frontend context-ring indicator was previously losing its percentage on every session load because the Session model silently dropped these fields when reconstructing from disk. (`api/models.py`, `api/routes.py`) @fxd-jason — PR #1341 (focused split from the held PR #1318)
+- **`fallback_providers` list config no longer crashes streaming** — `api/streaming.py:1701` previously read `_cfg.get('fallback_model')` and called `.get('model', '')` on the result. When users had `fallback_providers: [{...}, {...}]` in their config (the chained-fallback form documented in CHANGELOG since v0.50.151), the streaming path crashed with `AttributeError: 'list' object has no attribute 'get'`. Now consults both `fallback_model` (single dict, legacy) and `fallback_providers` (list, new), picks the first valid entry from the list, and defends both paths with `isinstance` checks. (`api/streaming.py`, `tests/test_pr1339_fallback_providers_list.py`) @jimdawdy-hub — PR #1339
+
+### Changed
+- **CI test stability** — `test_checkpoint_fires_on_activity_counter_increment` was rewritten to use deterministic `threading.Event` synchronization instead of `time.sleep` windows. The old version polled at 0.1s intervals and slept 0.15s/0.25s/0.25s between activity increments, which intermittently failed under CI scheduling jitter (one save instead of two). The new version waits up to 3.0s for the checkpoint thread to actually advance after each increment, with no sensitivity to scheduler timing. (`tests/test_issue765_streaming_persistence.py`)
+
+### Documentation
+- **`CONTRIBUTORS.md`** — new file with stack-ranked credit roll for all 66 contributors, generated from `git log` + `gh api` + CHANGELOG attribution lines. Top contributors table at top of `README.md`.
+- **README, ROADMAP, ARCHITECTURE, SPRINTS, TESTING** — refreshed to v0.50.246 / 3309 tests; removed stale `v0.50.36-local.1` header from ARCHITECTURE.md; updated SPRINTS.md "Where we are now" to reflect ~95% Claude parity. (PR #1340 — already merged, brought forward in this release.)
+
 ## [v0.50.245] — 2026-04-30
 
 ### Fixed