Add a session-scoped diagnostic console buffer and drawer for JavaScript and apiJson failures, with Jinja/JS copy mirrors, status-pane unread wiring, browser smoke coverage, and copy parity tests. API failures now enter the console at the apiJson chokepoint, and reportError can include bounded console-entry context in diagnostic bundles. Retire the auto-appearing bottom error strip in favor of the opt-in system messages drawer. This completes Phase 4 bucket 3 lode 5 of the convey-error-UX work. Co-Authored-By: Codex <codex@openai.com>