Fix three things found by actually using it

**The drag showed no tab.** Moving to pointer events lost the drag image
the OS used to supply, leaving a dimmed source tab and a 2px line —
which reads as "some setting changed", not "I am holding this tab". A
copy of the tab now follows the cursor, carrying its glyph and its real
label, grabbed at the offset it was picked up by so it sits where the
tab was.

**The URL relay opened a different URL than the one on screen.**
Observed: `repo.anhonesthost.net/…/tag/preview-63f3c54` arrived as
`repo.anhonsthost.nt/…/preview-63f3c54Butitprovesyournitpick…`. The
detector deleted *every* line break to undo PTY hard-wrapping, but a
terminal that wraps at a space emits the break **instead of** the space
— so deleting breaks also deletes the separators, gluing the following
paragraph onto the link and running the match past the host.

Only breaks the terminal inserted may be deleted, and those are exactly
the ones at the column width. The detector now takes a live column
getter and rejoins a line only when it is exactly that wide; every other
break becomes a space, which is also what stops a URL match. Lines
*longer* than the width are left alone — the stream had no break there,
so the one that follows is the application's own.

One case stays ambiguous: a URL whose length is an exact multiple of the
width is indistinguishable from one that was cut. That is pinned in a
test as known behaviour rather than papered over — the candidate is
shown in full and nothing opens without the user pressing Open.

**"In container" opened a page nobody could see.** It bound the browser
and stopped, leaving the user to find the Browser tab and press Start,
with nothing saying so — and from a terminal, no pane on screen at all.
Opening a page now starts the viewer if it isn't running, and the
terminal's prompt raises the pop-out window, because that caller has
nowhere else to put it.

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

app/src/lib/urlDetector.ts

@@ -3,8 +3,23 @@
  *
  * The Linux PTY hard-wraps long lines with \r\n at the terminal column width,
  * which breaks xterm.js WebLinksAddon URL detection. This class flattens
- * the buffer (stripping PTY wraps, converting blank lines to spaces) and
- * matches URLs with a single regex, firing a callback for ones >= 100 chars.
+ * the buffer (rejoining hard wraps, treating every other break as a
+ * terminator) and matches URLs with a single regex, firing a callback for ones
+ * >= 100 chars.
+ *
+ * ## Which line breaks may be deleted
+ *
+ * Only the ones the *terminal* inserted. A hard wrap happens at exactly the
+ * column width, so a line that reached the width was cut mid-token and its
+ * break must be removed to put the token back together; a line that stopped
+ * short ended for its own reasons and its break is a real separator.
+ *
+ * Deleting every break instead — which this did — glues unrelated output onto
+ * the end of a URL. Observed for real: a wrapped paragraph following a link
+ * became `…/tag/preview-63f3c54Butitprovesyournitpick…`, because a terminal
+ * that wraps at a space emits the break *instead of* the space, so removing
+ * the break removes the separator too. That candidate is a different URL from
+ * the one on screen, and the user is the one who has to notice.
  *
  * When a URL match extends to the end of the flattened buffer, emission is
  * deferred (more chunks may still be arriving). A confirmation timer emits
@@ -21,6 +36,45 @@ const MIN_URL_LENGTH = 100;
 
 export type UrlCallback = (url: string) => void;
 
+/**
+ * How wide the terminal is right now.
+ *
+ * A getter, not a number: the width changes with every window resize, and a
+ * stale one silently turns joining back into guesswork.
+ */
+export type ColumnsGetter = () => number;
+
+/**
+ * Rejoin the line breaks the terminal inserted; turn the rest into spaces.
+ *
+ * A line of exactly `columns` visible characters was cut by the terminal, so
+ * its break is deleted and the two halves are put back together. Anything
+ * shorter ended on its own and becomes a space — a URL cannot contain one, so
+ * that is also what stops a match running into whatever followed.
+ *
+ * `columns` of 0 or less means "not known yet"; nothing is rejoined, which
+ * costs a wrapped URL rather than inventing one.
+ *
+ * One case stays ambiguous and cannot be resolved here: a token that happens to
+ * end exactly at the width is indistinguishable from one the terminal cut, so
+ * the following line is joined to it. The candidate is still shown in full and
+ * confirmed by the user before anything opens.
+ */
+export function flatten(clean: string, columns: number): string {
+  const lines = clean.split(/\r?\n/);
+  let out = "";
+  for (let i = 0; i < lines.length; i++) {
+    out += lines[i];
+    if (i === lines.length - 1) break;
+    // `===`, not `>=`. A line *longer* than the width was never cut by the
+    // terminal — the stream simply contained no break there, so the break that
+    // follows it is the application's own and separates two things.
+    const wrapped = columns > 0 && lines[i].length === columns;
+    if (!wrapped) out += " ";
+  }
+  return out;
+}
+
 export class UrlDetector {
   private decoder = new TextDecoder();
   private buffer = "";
@@ -29,9 +83,11 @@ export class UrlDetector {
   private lastEmitted = "";
   private pendingUrl: string | null = null;
   private callback: UrlCallback;
+  private columns: ColumnsGetter;
 
-  constructor(callback: UrlCallback) {
+  constructor(callback: UrlCallback, columns: ColumnsGetter) {
     this.callback = callback;
+    this.columns = columns;
   }
 
   /** Feed raw PTY output chunks. */
@@ -61,12 +117,8 @@ export class UrlDetector {
     // 1. Strip ANSI escape sequences
     const clean = this.buffer.replace(ANSI_RE, "");
 
-    // 2. Flatten the buffer:
-    //    - Blank lines (2+ consecutive line breaks) → space (real paragraph break / URL terminator)
-    //    - Remaining \r and \n → removed (PTY hard-wrap artifacts)
-    const flat = clean
-      .replace(/(\r?\n){2,}/g, " ")
-      .replace(/[\r\n]/g, "");
+    // 2. Flatten the buffer: rejoin hard wraps, terminate on everything else.
+    const flat = flatten(clean, this.columns());
 
     if (!flat) return;