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No.214 · Developer· New

Log Tail

A live log that follows new lines until you scroll up, then holds still and counts what arrived. Level filters with counts, pattern highlighting that falls back to plain text on a broken regex, clock or relative times, and only the visible rows rendered.

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Written for the variant you picked above: Light

Build a streaming log viewer for a fictional 'masar-api · production'. Lines are { id, t, level: debug|info|warn|error, source, msg }; the parent appends to the array and the view reacts. Layout: a 12px-radius panel in IBM Plex Sans with IBM Plex Mono for the log. Toolbar: the title with a small green dot that pulses while following, four level toggle chips (uppercase mono, each with its count, tinted by level when on: grey, blue, amber, red; debug starts off), a regex search field, an 'Only matches' checkbox and a Clock/Relative time toggle. Under it a one-line note: the match count, or why the pattern is invalid ('missing ), searching literally'). The log is a bordered mono area with 22px rows: time (HH:MM:SS.mmm or '12s ago'), the level in bold colour, the source with a › and the message, ellipsised. Error rows get a faint red wash; matches get a yellow mark. Windowing: a spacer of rows × 22px with only the rows in view (plus 8 overscan) absolutely positioned. Follow: while scrolled to the bottom, new lines keep it pinned; scrolling up pauses, new lines are marked with a blue left rule and a floating pill shows '12 new ↓'; clicking it or scrolling to the end resumes. A footer says 'Following new lines' or 'Paused at line 412 of 640'. Selected variant — Light (light): Palette for this theme (Light): --ltail-bg #fbfbf9; --ltail-debug #7a7f88; --ltail-error #c8331f; --ltail-error-bg rgb(200 51 31 / 0.06); --ltail-focus #2f6fd0; --ltail-info #2f6fd0; --ltail-ink #1b1c1f; --ltail-line rgb(27 28 31 / 0.09); --ltail-live #22a06b; --ltail-mark #ffe58a; --ltail-mark-ink #1b1c1f; --ltail-muted #6b6f77; --ltail-new rgb(47 111 208 / 0.08); --ltail-panel #ffffff; --ltail-warn #b07605. Treat these as the root colour tokens, one value per role, and name them to suit your code. Select it with the theme option set to "light". Keep every dimension, spacing value, state and motion from the brief unchanged, and keep text at 4.5:1 contrast or better on these surfaces. This selection takes precedence over references to other themes or options in the general brief. Implement this selected appearance; do not add a variant picker or alternative appearances unless requested. Implementation requirements: Use React and TypeScript. Keep the component self-contained, with uniquely scoped CSS and no animation libraries. Include required imports, styles and font setup in the result. Interaction: Scroll up to pause and down to the end to resume, or click the 'new ↓' pill. Chips toggle levels; typing highlights matches; the checkbox hides non-matching lines; the time button switches format. The log area is focusable for keyboard scrolling. Motion: The live dot pulses only while following; the pill fades up when it appears. Both stop with reduced motion. Accessibility: The log has role=log with aria-live off, so streaming lines are not read aloud; a polite footer reports follow or pause, and the match count or regex error is announced. Level chips use aria-pressed; the search field marks an invalid pattern. Responsive behavior: Below 640px the search takes a full row, times narrow and sources hide. Touch: Touch scrolling pauses and resumes the same way; the pill is a large tap target. Preserve keyboard access, visible focus and reduced-motion behavior. Keep fictional demo data and simulated service calls in a separate usage example; expose callbacks for real actions and recover from rejected requests. Keep usage-example links inside the demo: use local buttons or prevent navigation. Demonstration links must not navigate to Vitrine routes or open other pages; preserve real URL support in the reusable component itself. Verify the result at narrow and wide viewport sizes, with keyboard input and reduced motion enabled.

Notes

Interaction
Scroll up to pause and down to the end to resume, or click the 'new ↓' pill. Chips toggle levels; typing highlights matches; the checkbox hides non-matching lines; the time button switches format. The log area is focusable for keyboard scrolling.
Motion
The live dot pulses only while following; the pill fades up when it appears. Both stop with reduced motion.
Accessibility
The log has role=log with aria-live off, so streaming lines are not read aloud; a polite footer reports follow or pause, and the match count or regex error is announced. Level chips use aria-pressed; the search field marks an invalid pattern.
Responsive
Below 640px the search takes a full row, times narrow and sources hide.
On touch
Touch scrolling pauses and resumes the same way; the pill is a large tap target.

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