fix(terminal): ship the copy clean as a trailing trim, without the shared dedent

#451 cleaned two things on copy. The trailing trim is right and every native
terminal does it. The shared leading-indent strip is this project's own rule,
and it is dropped here rather than shipped.

Measured against the shipped transform over 401,445 three-row windows across
1,010 tracked files in this repo, it fired on 73% of them: 92% inside a YAML
workflow, 76% over `git log` output, 48% in a TypeScript source. No width
threshold separates a margin from content because they are the same widths, a
live Claude Code pane's own margins measuring 2 and 5 columns while the most
common non-TUI shared run is 4. The failure modes are not symmetric either: a
wrong trailing trim costs nothing, while a wrong dedent silently deletes
information that was on the screen, with nothing in the clipboard to hint at
it, on git log bodies, on indented code read out of cat (semantic in Python),
on git diff context rows where the leading space is the marker, and on stack
traces.

It also could not be made self-consistent cheaply. Whether the first row joined
the measurement depended on the mousedown COLUMN, which the user never sees, so
one block of three rows produced three different clipboard results; and the
flag read getSelectionPosition().start, which is xterm's mousedown anchor and
is never normalised, so dragging UP through a block read it off the bottom row.
The PR's test stub hardcoded a downward drag, so its suite could not express
that case.

The transform, the wiring, the tests, the invariants, CLAUDE.md, the wiki page
and the changeset all move together. The test block now pins the ABSENCE as a
contract, with the git log, Python and git diff cases as its examples, so this
is not re-derived later. If it is ever revisited, the one qualification that
measured clean is painted trailing padding: zero false positives over all
401,445 windows.

Also from the review: the comments and invariant rule justifying the
padding-only clear described the pre-change code (the Ctrl+C gate reads the
CLEANED selection now, so such a selection falls through to the PTY on its own
and the clear is feedback rather than protection), the new 'Nothing to copy'
toast gained its zh-CN entry, and the invariants paragraph no longer repeats
its own opening sentence.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -318,7 +318,7 @@ Frontend JS modules have `@fileoverview` with `@dependency`/`@loadorder` tags. L
 
 **Welcome "Resume Conversation" list** (terminal-ui.js): `loadHistorySessions()` fetches once and caches the corpus on `_historyAll`/`_historyCases`; every subsequent view (filter box, sort select, expand, the periodic refresh in panels-ui.js) goes through `_renderHistoryList()`, so never append rows to `#historyList` directly or re-fetch to re-sort. ⚠️ The box height is **class-driven**: expanding the list without `.history-list.expanded` leaves the collapsed `max-height` in place and just deepens a scroll well, which is the bug #260 reported (35 sessions in a ~4-row box). ⚠️ The A–Z sort keys off `_historyRowLabel()`, the SAME string the row renders (`name || firstPrompt || path`), most rows are transcript-backed and have no session name, so sorting on `name` alone silently does nothing. ⚠️ A filter implies expansion, and `_renderSearch()` hides `#historyHeader` (title + controls) as one unit while a search is active. Tests: `test/history-list-controls.test.ts`.
 
-**Command palette + shortcut registry**: `Ctrl/Cmd/Alt+K` opens the session palette; shortcuts live in a rebindable registry (`DEFAULT_SHORTCUTS`/`getShortcutRegistry()`/`matchesShortcutEvent()` in app.js, overrides in `settings.shortcutOverrides`). ⚠️ Palette-chord keys must ALSO be swallowed in `attachCustomKeyEventHandler` (terminal-ui.js) or xterm writes the control byte (0x0B) into the PTY. ⚠️ `saveAppSettings()` rebuilds settings from the DOM, so keys edited elsewhere (`shortcutOverrides`, `showTokenCount`, `showCost`) need explicit `_prev` carry-over. ⚠️ **Smart copy (`Ctrl+C`)** lives in that same handler: with a selection it copies, with none it must `return true` **without** `preventDefault()` or the interrupt is lost. `copyTerminalSelection` is deliberately absent from `SHORTCUT_ACTIONS` because the generic capture loop preventDefaults every match it dispatches. → [architecture-invariants#command-palette-and-shortcut-registry](docs/architecture-invariants.md#command-palette-and-shortcut-registry)
+**Command palette + shortcut registry**: `Ctrl/Cmd/Alt+K` opens the session palette; shortcuts live in a rebindable registry (`DEFAULT_SHORTCUTS`/`getShortcutRegistry()`/`matchesShortcutEvent()` in app.js, overrides in `settings.shortcutOverrides`). ⚠️ Palette-chord keys must ALSO be swallowed in `attachCustomKeyEventHandler` (terminal-ui.js) or xterm writes the control byte (0x0B) into the PTY. ⚠️ `saveAppSettings()` rebuilds settings from the DOM, so keys edited elsewhere (`shortcutOverrides`, `showTokenCount`, `showCost`) need explicit `_prev` carry-over. ⚠️ **Smart copy (`Ctrl+C`)** lives in that same handler: with a selection it copies, with none it must `return true` **without** `preventDefault()` or the interrupt is lost. `copyTerminalSelection` is deliberately absent from `SHORTCUT_ACTIONS` because the generic capture loop preventDefaults every match it dispatches. ⚠️ **The gate tests the CLEANED selection, not the raw one** (`CodemanCopySelection.clean` in constants.js, pure; `cleanedTerminalSelection()` reads the live terminal): xterm returns whole screen ROWS and trims only never-written cells, so the spaces a full-screen TUI paints across the rest of a row are content and reach the clipboard (138 of them per line, measured in a 282-column pane). The clean drops each line's TRAILING run and nothing else. ⚠️ **A shared LEADING indent is deliberately NOT stripped**, and that is a decision, not a gap: it was built, measured and dropped before #451 merged, because it fired on 73% of real non-TUI text (401,445 windows sampled) and no width threshold separates a TUI margin from content (a claude pane's own margins are 2 and 5 columns; the commonest non-TUI shared run is 4). Do not re-add it without reading the rule in architecture-invariants. ⚠️ Alt+drag COLUMN selections are returned untouched (`_activeSelectionMode === 3`), and the padding-only clear is FEEDBACK rather than interrupt protection, since a padding-only selection now cleans to `''` and falls through to the PTY on its own. → [architecture-invariants#command-palette-and-shortcut-registry](docs/architecture-invariants.md#command-palette-and-shortcut-registry)
 
 **Per-device vs synced settings**: the `displayKeys` set in settings-ui.js is a **client-side merge policy**, not a wire filter. A display key seeds from the server only when localStorage has no value for it, which is what prevents one device overwriting another; `showPlanUsageLimits` is additionally `delete`d from the incoming payload outright. Separately, `SettingsUpdateSchema` is `.strict()` and simply **does not declare** `skin`, `showFileViewerButton`, `showCronButton`, `webglRendererEnabled`, `localEchoEnabled`, `cjkInputEnabled`, or `extendedKeyboardBar`, so sending one of those is a validation error. The rest (`showResponseViewer`, `showPlanUsageLimits`, `language`, and most `show*` keys) ARE in the schema and do persist server-side; they are per-device by client policy only. ⚠️ Adding a new per-device setting means deciding **both** questions: membership in `displayKeys`, and presence in the schema.