v0.15.0

Lit Inspector is on the Chrome Web Store, and the Timeline now explains itself:
every update records what caused it, a column of rails draws the chain from a
click or a parent render through @lit/task runs to the re-render, and a time
range can be selected, summarised and shared as a link. The Components tab
shows a component's slots, parts, context, Lit's warnings and tags that were
never defined, and its details pane can be filtered, folded, expanded and
copied from. Nothing needs action to upgrade.

Added

• Lit Inspector is on the Chrome Web Store. Install it with Add to Chrome
  instead of loading an unpacked zip, and Chrome keeps it up to date. Firefox
  still loads the zip from the GitHub release.
• Updates know what caused them. The cause is recorded at the
  requestUpdate call that scheduled an update, so the Updates tab reads
  "after click (412, 88)" or "after my-parent update" instead of guessing from
  timing, and the Timeline details pane names the cause with a show link to it.
• The Timeline draws why each update ran. A column beside the list connects
  an update to the row that caused it: the parent whose render set a property
  on it, or the click, key or custom event whose handler requested it. Rows
  stay in time order, each chain has its own colour, and hovering a row
  highlights its chain.
• @lit/task runs show in the Timeline's cause chain. A task run is a row
  of its own, from the update or handler that started it to when it settled,
  and the re-render it asks for hangs from it, so a click, the fetch it started
  and the render that showed the result read as one chain.
• Select a time range in the Timeline. Shift+drag on the tracks, or drag
  the time ruler, to see which layers fired and which components updated in
  that stretch, then zoom to it or filter the list to it. Drag either edge, or
  Tab to it and use the arrow keys, to adjust it a tick step at a time; Shift
  moves five.
• Share a Timeline range as a link. Copy link in the range summary gives an
  address with #tab=timeline&range=<start>-<end> that opens the Tracks on
  that stretch, including in an exported snapshot.
• Coding agents can summarise a window of the Timeline. The new
  lit_range-summary MCP tool takes a start and an end from
  lit_recent-events times and returns which layers fired and which components
  updated between them.
• See a component's slots and parts. The Components tab lists each slot
  with what is assigned to it, flags empty, fallback, forwarded and duplicate
  slots, and shows in red the children no slot takes. Turn on Anatomy to draw
  the slots and ::part exports on the page; hovering a row in the Slots or
  Parts table pulses that region and fades the others.
• See parts forwarded with exportparts. The Parts list and the Anatomy
  overlay now include parts a nested component re-exports, marked forwarded,
  and show the outer name when exportparts renames one.
• See which provider a Lit context consumer reads from. The Components
  details pane now shows each @lit/context provider and consumer with its key
  and value, links a consumer to its provider and a provider to its consumers,
  and selects the element when you click a link.
• Record the custom events your components dispatch. The new Custom events
  layer on the Timeline, off by default, shows each event's type, flags and
  detail next to the component that dispatched it.
• Lit dev-mode warnings show up. Mistakes Lit warns about, like scheduling
  an update from inside updated(), record a warning event in the Timeline
  naming the component, including ones issued before recording started. A
  component Lit has warned about gets a warning chip and a Warnings section in
  the Components tab, with Lit's message and a link to its explanation; agents
  get the same list from the component details tool.
• Updates that shouldUpdate vetoes leave a trace. A refused update
  records an update skipped event in the Timeline with the property keys that
  changed, and the Updates tab counts each component's refused updates and
  marks them in its list.
• Components that were never defined show up in the tree. A custom tag on
  the page with no definition, from a missing import or a typo, is listed with
  a "not defined" chip instead of being left out; selecting it explains what is
  missing and links to the template that renders it. Agents see it in the
  list-components tool too.
• Property options show on the Properties rows. A custom hasChanged or
  converter, noAccessor, useDefault and attribute: false each get a
  badge, so you can see how a property is declared without opening the source.
  lit_component-details lists the same options for agents.
• Filter the Components tree. A box in the toolbar narrows the tree to
  elements whose tag or class name matches, keeps their parents for context,
  and restores your expanded branches when cleared.
• Filter the details pane. A box under the tag name narrows properties,
  state, attributes, instance fields, slots and parts to rows whose name or
  value matches, and stays set as you select other components.
• Details sections fold, and remember it. Properties, State, Attributes,
  Instance, Slots and Parts each fold on their heading, show how many rows they
  hold, and stay folded as you select other components.
• Expand values in the details pane. Objects, arrays, Maps and Sets open
  level by level from a caret, so values nested past the preview limits are no
  longer cut off, and open levels follow the value as it changes. Maps and Sets
  also preview their first entries, such as Map(2) {"a" => 1, "b" => 2}.
• Values in the details pane are syntax-coloured and pretty-printed.
  Strings, numbers, keywords and keys are coloured like code, and objects or
  arrays too wide for a line show one entry per line.
• Changed values light up in the details pane. When the selected component
  updates, each row whose value changed briefly highlights, so you can see what
  an interaction touched.
• Copy a value from the details pane. Hover a row for a copy button that
  puts the value, as shown, on the clipboard.
• Shift-hover a tree row to outline every instance of that component. The
  page shows each element with the same tag in a dashed box, and the tree marks
  their rows.

Changed

• Timeline list rows group by update. Each component update is one
  collapsed row showing its duration and changed properties; expand it to see
  its phases, skips, warnings and events from the same update.
• The Timeline's detail pane is resizable and easier to scan. Drag its top
  edge to give a selected event more room; the height sticks. A header shows
  the event's name, layer, time and duration, and the facts below line up in a
  compact grid with pretty-printed data and any recorded error.
• The Components details header is compact. The class and template
  locations, and the render root, now sit in a three-line block under the tag
  name, and a status shows next to the tag only while an update is pending or
  the first render has not happened.
• Long values in the details pane get the full width. Objects and long
  strings move to their own line instead of wrapping in a narrow column, badges
  follow the value, and arrays, dates and DOM nodes are tagged with their type.
• Task status shows as a coloured dot in the details pane. Instance rows
  name their kind in a quiet tag after the name instead of outlined chips, a
  task's status is green, amber or red, and attribute values show as quoted
  strings.
• Details sections are easier to tell apart. A thin rule and more space now
  separate Properties, State, Attributes, Instance, Slots and Parts.
• The Anatomy toggle is remembered. Leaving it on keeps it on after the
  panel reloads.

Fixed

• The Slots table follows light-child changes. Changing a child's slot
  attribute, or adding or removing children, now updates the selected element's
  slots without a re-render or a re-select.
• Timeline ticks line up with the marks. With many lanes and a scrollbar,
  the time ruler was offset from the marks by the scrollbar's width, and the
  range edges could block clicks on marks beneath them.
• The Timeline range no longer overshoots the tracks. With many lanes and a
  vertical scrollbar, the shaded range's right edge stopped a few pixels past
  the last mark; it now ends where the marks do.
• Long strings in the details pane wrap under their own text. A string that
  wraps inside a pretty-printed object now continues indented under its line
  instead of at the left edge of the value.