docs(process): clarify normalized terminal row geometry

docs/process-capture.md

@@ -110,11 +110,13 @@ while comparisons and trace assertions use the normalized text. Retaining the
 original adds at most `limits.output_bytes` of text, because it comes from the
 same admitted PTY chunks rather than a second unbounded stream.
 
-Rendered frame `lines` hold the visible rows after normalization, without
-trailing spaces; pad a line to the frame's `columns` to restore the fixed-width
-row. `serialized_state` keeps the exact terminal state. Captures commit this
-line format in their comparison contract, so a capture whose lines were padded
-to full width does not compare as the same contract.
+Rendered frame `lines` hold the normalized visible rows with trailing U+0020
+spaces removed. `columns` records the original terminal geometry. Normalization
+can change text length, so restoring an earlier normalized row's padding requires
+information beyond `columns`. `serialized_state` retains the normalized terminal
+serialization. Captures commit this line format in their comparison contract, so
+a capture whose lines were padded to full width does not compare as the same
+contract.
 
 Port normalization recognizes explicit `port`, `tcp_port`, `udp_port`, and
 `listen` fields, URL authorities, IP endpoints, and `localhost` endpoints, with

src/process/capture/TerminalRenderer.test.ts

@@ -26,7 +26,7 @@ it("omits trailing blank cells from visible lines without losing rows", async ()
   );
   const [frame] = frames;
   expect(frame?.lines).toEqual(["left  right", "", "  indented", ""]);
-  // Fixed-width rows remain recoverable from the recorded column count.
+  // These plain rows use identity normalization and can be padded for display.
   expect(frame?.lines.map((line) => line.padEnd(frame.columns, " "))).toEqual([
     "left  right         ",
     " ".repeat(20),

src/process/capture/TerminalRenderer.ts

@@ -108,8 +108,8 @@ export class TerminalRenderer {
     const lines: string[] = [];
     for (let row = 0; row < this.#terminal.rows; row += 1) {
       const line = buffer.getLine(buffer.viewportY + row);
-      // Trailing blank cells carry no information beyond `columns`; dropping
-      // them keeps sparse screens from costing a full row per blank line.
+      // Keep normalized display text compact. It can differ in length from the
+      // original terminal geometry recorded by `columns`.
       lines.push(
         this.options
           .normalize(