The buy shelf can say what is under a point: a cursor as data and a `controlAt` lookup #421

This is the first half of #355: the buy shelf can now say which control is under a point. Nothing is wired in yet, so main.ts and the game behave exactly as before. The #355 branch named in the issue no longer exists, so I started from pull #358's head (refs/pull/358/head) and reshaped its code to the design in #418.

• src/client/cursor.ts (new): the buy panel's own pointer as plain data, { x, y, area }.

- cursorIn(box) puts it at the centre of a rectangle. A rectangle with no size holds it at its corner rather than at NaN. - move(cursor, dx, dy) moves it one pixel per count of mouse movement, clamped to all four edges. A move that isn't a number moves nothing. - toCounts(degrees, sensitivity) turns the sensitivity-scaled look the frame receives back into counts. The pointer's speed then doesn't depend on the sensitivity. It isn't in the issue's list, but the wiring half needs it.

• src/client/buy.ts: drawBuy now returns each control it drew as { tile, box(), act }. act is the same function the click listener calls, so a press through the pointer is a click.

- controlAt(drawn, x, y) returns the live control under a point. It returns null over a greyed tile, a gap, anything outside the panel, or a point that isn't a number. - A box includes its left and top edges but not its right and bottom ones, so two touching tiles never both answer. - The box is read each time controlAt runs, not when the panel is drawn. main.ts draws the panel before showing it, and a hidden panel has no layout yet.

• Unchanged on purpose: #358 rewrote the hint text, which would have broken an existing test, so the hint stays as it is. Its version of controlAt took an element from elementFromPoint; this one takes a point, as the issue asks. Drawing the arrow and sending the mouse to it belong to the second half.

Tests: in cursor.test.ts, the start position, movement, clamping at each edge and corner, and sensitivity. In buy.test.ts, controls come back in draw order with their presses, and points over a live tile, the rebuy control, a greyed tile, a gap, outside the panel and an unlaid-out page. The existing buy tests are untouched apart from the import line. bun run test (typecheck, then bun test) passes: 1734 tests.

To try it: run bun test src/client/cursor.test.ts src/client/buy.test.ts. The preview looks the same as production.

🤖 Generated with Claude Code

Closes #418

After #420 put all of #358 on main, this pull shrank to two things: a clamping test for the buy panel's pointer, and a fix that brings / back inside its size budget. #420 landed cursor.ts, controlAt and the wiring in main.ts, which covers what #418 set out to build. That is also why this branch conflicted.

• Merge: I kept main's versions of the four conflicting files, because main.ts is built on them. main already uses centre, moveCursor and toPixels, and controlAt over an element from elementFromPoint. This branch's point-based API would have been a second, unused way to do the same thing. Switching main.ts over to it would have gone against #418's "no change to main.ts".
• Kept from this branch: a test in src/client/cursor.test.ts that clamps moveCursor at each of the four edges separately. It also checks that the way back from a pinned edge starts at the edge.
• Budget fix: main itself fails "a first visit stays inside its byte budget": with #419 and #420 together, / sends 10,646 B gzipped against a 10,500 B budget.

- styleFor in src/pages/shell.ts now strips CSS comments before the style block is sent and hashed. Stripping in that one place keeps the page and the style-src hash in step. - The page's style block drops from 7,757 to 7,055 bytes raw, and / is back inside its budget. - A new test in src/pages/shell.test.ts checks that comments are removed from the block and from the page. - No test and no budget changed, and the #419 and #420 wording is untouched.

bun run test (typecheck, then bun test) passes: 1742 tests. To try it, open / in the preview and view the source: the <style> block has no comments and the page looks the same. The buy pointer behaves as it does on main.

🤖 Generated with Claude Code

This pull now only adds two tests. main has since shipped everything else it was going to change: #420 brought in the buy panel's pointer (cursor.ts, controlAt and the main.ts wiring). #410 made the shell strip CSS comments from the style block before it is sent and hashed, which is what this branch had done to keep / inside its byte budget.

• Merge: I took main's src/pages/shell.ts as it is. Its uncommented does the same job as this branch's, also trims the spaces around a comment, and is documented. Keeping both would have been two copies of one function.
• src/pages/shell.test.ts: a test that a page's CSS comments are removed from the style block and from the page. main had no test for this. Its expected string drops the trailing space, because main's version trims the spaces around a comment; that follows main's intended behaviour and does not mark a bug.
• src/client/cursor.test.ts: a test that moveCursor stops at each of the four edges separately. It also checks that moving back from a pinned edge starts at the edge.

No code changes remain relative to main. bun run test (typecheck, then bun test) passes: 1755 tests. To try it, run bun test src/pages/shell.test.ts src/client/cursor.test.ts.

🤖 Generated with Claude Code