Reader: the tail is the paragraph rhythm, not a 30px reserve

[lvwerra]

it seems like there is an additional newline at the end of the reader view. just a bit too much whitespace imo. can you have an agent confirm and fix?

Confirmed. Measured before/after →

Scrolled to the end of a conversation that fills the pane, the space between the last line and the composer's border was 2.7× the spacing between the paragraphs above it:

	last line → composer	between paragraphs
desktop, before	32px	12px
phone, before	26px	12px
both, after	14px	12px

What it was — and the three things it wasn't

You were right to point at 633d492's class of cause, so I checked those first and each is ruled out by measurement, not by reasoning:

• Not an uncollapsed margin. The last rendered block reports margin-bottom: 0px — .cx-md > :last-child already gives it up.
• Not a trailing empty node from the renderer. Nothing renders after the last paragraph at all: I enumerated every element whose box ends at or below it and the list is empty.
• Not an element with no content. No spacer, no blank pending exchange, no working line with nothing to say — the shape that caused both earlier reports (Reader: the middle of a turn is markdown too #88's empty head row, Reader: the answer where it was said, one working line, a still turn column #85's blank meta half) is simply not present here.

It was .cxv-body's own bottom padding: 30px (24px on a phone), sitting in the same shorthand as the reading gutter:

.cxv-body { --cx-gutter: 14px; … padding: 4px var(--cx-gutter) 30px; }

A number from when the reader's bottom edge was the pane's, before a composer sat under it with a border 30px away. So a margin fix would have been the wrong shape of fix — but so would trimming it by eye.

The fix, and where the number comes from

--cx-tail: 12px — the same 12px that separates two paragraphs (.markdown p { margin: 0 0 12px }). The end of the flow is then spaced like the flow: 14px in total on both viewports, the tail plus .cx's own 2px.

The phone rule restated the whole shorthand in order to narrow the gutter, and carried a different bottom (24px) as a side effect. With the tail a variable it has nothing left to restate — it narrows --cx-gutter and nothing else, which is the same drift this file already learned about with the prompt band's bleed in #71.

The two things that must not break

• It still opens on the last exchange with the newest content on screen (Trace reader: open on the last exchange, page backwards by byte window #55/Reader: come back to where you were reading #59). At 1180px and at 390pt: atBottom: 0, last exchange fully visible, its answer on screen. Scrolling to the top and back returns to the end with the same 14px.
• Surface native TUI input requests in readers #78's needs-input band composes with it. That band is not on main, so I merged refs/pull/78/head in locally to check (clean merge, nothing pushed). It sits last inside the scroller with margins 8px/2px: 10px above it, and 14px below — its own 2px plus the tail, carrying no reserve of its own. Before this change that state had 32px under the band too, so the band was not the thing holding the extra space.

Pinned

In web/test/pendingExchange.test.mjs, where the reader's other CSS invariants live:

• the tail comes from --cx-tail, not a number in the shorthand;
• its value equals .markdown p's bottom margin — the relationship, not the coincidence, so the two cannot drift apart silently;
• the phone rule restates no padding;
• and the last rendered block still gives up its own margin.

Mutation-checked: restoring the 30px tail fails two of those, restating the phone padding fails the third.

Suites

Web green (143 checks), typecheck clean. server/test/archive.test.mjs and resize.test.mjs each failed in a full run and behave identically on pristine main under the same load: archive passes alone on both trees, and resize fails alone on both (2 failures, same assertions, with five other agents' servers running). Neither is related to this change, which is CSS in the reader.

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