Give the prompt one blank row of bottom breathing room (CL-5619)

CHANGELOG.md

@@ -21,6 +21,10 @@ Format loosely follows [Keep a Changelog](https://keepachangelog.com/). Versions
 
 ### TUI
 
+- **Bottom breathing room.** The prompt box sits one blank row above the
+  terminal's last line on terminals tall enough to spare it
+  (`BOTTOM_MARGIN_ROWS`, collapsed below 24 rows), so the layout no longer
+  feels flush against the frame edge.
 - **Drag-select auto-copy.** With mouse capture on (the default), finishing a
   drag selection in the transcript writes the selected text to the system
   clipboard on mouse-up and flashes a short status line. Alt+M still hands the

docs/TUI.md

@@ -45,6 +45,14 @@ middle tier: one column is already enough to keep content off the frame edge,
 which is the gutter's entire job, and anything wider only read as excess air on
 a wide pane. The gutter costs no rows.
 
+Vertically, the same file keeps content off the top and bottom edges with one
+blank row each: `TOP_PAD_ROWS` above the first transcript row, and
+`BOTTOM_MARGIN_ROWS` below the prompt box. Both are carved out of the
+transcript residual by the shell after the geometry resolver has assigned
+heights, so they never change the resolver's row budget. Each collapses to
+zero when the terminal is too short to spare it (`TOP_PAD_MIN_TRANSCRIPT_ROWS`
+for the top pad, `BOTTOM_MARGIN_MIN_ROWS` for the bottom).
+
 The prompt box's border carries the metadata that would otherwise cost a
 titlebar row: the model label sits right-aligned in the top rule; the brand
 lockup sits at the left of the bottom rule with the working directory and git

src/tui/geometry/margins.ts

@@ -1,12 +1,12 @@
 /**
  * Optical breathing room shared by every shell surface.
  *
- * The margin is one number for the whole interface — transcript, prompt box,
- * model bar, hint row and overlay host all sit inside it — so the shell reads
- * as a single column of content rather than panes that happen to be stacked.
- *
- * Horizontal only. The row budget is the geometry resolver's business; nothing
- * here can take a row away from it.
+ * The side gutter is one number for the whole interface — transcript, prompt
+ * box, model bar, hint row and overlay host all sit inside it — so the shell
+ * reads as a single column of content rather than panes that happen to be
+ * stacked. Top and bottom pads are carved out of the transcript residual by
+ * the shell after the geometry resolver has assigned heights, so they never
+ * change the resolver's row budget.
  */
 
 /**
@@ -50,14 +50,14 @@ export function resolveTopPadRows(transcriptRows: number): number {
 }
 
 /**
- * Rows below the prompt box. Zero: the box sits on the terminal's last row.
+ * Rows below the prompt box once the terminal can afford them.
  *
- * A blank row here reads as the interface floating rather than resting on the
- * bottom edge — the box is the thing the operator types into, and it wants to
- * be where the cursor already is. The side gutters still keep it off the left
- * and right edges, which is where crowding actually shows.
+ * One blank row keeps the prompt off the terminal's last line the same way
+ * `TOP_PAD_ROWS` keeps the first transcript row off the top edge and
+ * `SIDE_MARGIN` keeps content off the left and right. More than one only
+ * reads as the interface floating, so there is no middle tier.
  */
-export const BOTTOM_MARGIN_ROWS = 0
+export const BOTTOM_MARGIN_ROWS = 1
 
 /**
  * Below this terminal height the margin is not worth the row it costs — the

src/tui/landing.test.ts

@@ -382,9 +382,10 @@ describe("landing screen", () => {
           row.includes(LOCKUP_WORDMARK),
         )
         // Session-active: the version row only reserves space on the landing
-        // screen (see `relayout`), so once there is real transcript content
-        // the box is back on the terminal's very last row.
-        expect(ruleRow).toBe(SIZE.height - 1)
+        // screen (see `relayout`). Once there is real transcript content the
+        // box sits one row above the terminal's last line — the optical
+        // bottom pad (`BOTTOM_MARGIN_ROWS`) keeps it off the frame edge.
+        expect(ruleRow).toBe(SIZE.height - 2)
         const row = painted[ruleRow]!
         // Left end of the rule, inside the shell gutter, costing no row.
         expect(row.startsWith(" ╰─ ")).toBe(true)

src/tui/landing.ts

@@ -62,11 +62,10 @@ export const LANDING_VERSION = `v${pkg.version}`
  * Minimum terminal size the version badge needs before it hides. 16 rows is
  * above `IDLE_TRANSCRIPT_FLOOR` (12) — the only row floor real chrome is
  * actually held to at rest — so the badge is gone well before the
- * transcript itself would be squeezed. It is below `BOTTOM_MARGIN_MIN_ROWS`
- * (24, in `geometry/margins.ts`); that constant does not currently mean
- * anything in practice (`BOTTOM_MARGIN_ROWS` it gates is 0), so there is no
- * real floor at 24 to be above yet, but if one is ever added there this
- * threshold does not automatically clear it and should be revisited.
+ * transcript itself would be squeezed. It is also below
+ * `BOTTOM_MARGIN_MIN_ROWS` (24): the bottom pad is optical room carved from
+ * the transcript residual, not a second reserved chrome row, so the badge's
+ * own threshold does not need to clear it.
  */
 export const VERSION_BADGE_MIN_COLUMNS = 60
 export const VERSION_BADGE_MIN_ROWS = 16

src/tui/margins.test.ts

@@ -1,7 +1,7 @@
 /**
  * Breathing room: one optical gutter shared by every surface, a blank row above
- * the first transcript row, and a narrow-terminal floor where the gutter yields
- * to content rather than squeezing it.
+ * the first transcript row, a blank row below the prompt box, and a
+ * narrow-terminal floor where each pad yields to content rather than squeezing it.
  */
 import { describe, expect, test } from "bun:test"
 import {
@@ -107,7 +107,15 @@ describe("top padding", () => {
 })
 
 describe("bottom edge", () => {
-  test("the prompt box rests on the terminal's last row", async () => {
+  test("one blank row below the prompt once the terminal can afford it", () => {
+    expect(resolveBottomMarginRows(BOTTOM_MARGIN_MIN_ROWS)).toBe(1)
+    expect(resolveBottomMarginRows(30)).toBe(1)
+    expect(resolveBottomMarginRows(60)).toBe(1)
+    expect(resolveBottomMarginRows(BOTTOM_MARGIN_MIN_ROWS - 1)).toBe(0)
+    expect(resolveBottomMarginRows(12)).toBe(0)
+  })
+
+  test("the prompt box leaves a blank row above the terminal's last line", async () => {
     await withTestRenderer(
       async (h) => {
         const shell = createAppShell(h.renderer, {
@@ -118,9 +126,14 @@ describe("bottom edge", () => {
           appendStreamRow(shell, { role: "user", text: "check the bottom" })
           await settle(h)
           const rows = frameRows(h)
-          // The box is what the operator types into; it belongs where the
-          // cursor already is, not floating a row above it.
-          expect(rows[rows.length - 1]?.trim()).not.toBe("")
+          // One optical row under the box — same job as the top pad and the
+          // side gutters, just at the other edge.
+          expect(shell.bottomPad.visible).toBe(true)
+          expect(shell.bottomPad.height).toBe(1)
+          expect(rows[rows.length - 1]?.trim()).toBe("")
+          // The box itself still paints: its bottom rule is the last content
+          // row, not the last terminal row.
+          expect(rows[rows.length - 2]?.includes("╰")).toBe(true)
         } finally {
           shell.dispose()
         }
@@ -137,7 +150,6 @@ describe("bottom edge", () => {
     }
   })
 
-
   test("collapses to zero on a short terminal so nothing else starves", async () => {
     const rows = BOTTOM_MARGIN_MIN_ROWS - 1
     await withTestRenderer(

src/tui/shell.ts

@@ -774,8 +774,9 @@ function terminalOf(
 
 /**
  * The version row is real chrome, not a float — it holds its own reserved
- * row at the foot of the shell rather than overlaying content that already
- * fills every row (there is no other spare one; `BOTTOM_MARGIN_ROWS` is 0).
+ * row at the foot of the shell rather than painting into the optical bottom
+ * pad (`BOTTOM_MARGIN_ROWS`), which is blank breathing room, not a content
+ * slot.
  *
  * This genuinely costs the rest of the shell a row, not just the space it
  * paints in: the geometry resolver is handed `terminal.rows - 1`, so every