feat(tui): wipe in first generated titles - #41903

What

The left-to-right title wipe removed in #40318 returns, gated and feathered: when a session's first real title arrives, it wipes in over the placeholder instead of popping.

Stacked on #41921 (dim placeholders), which supplies the placeholder predicate the gate uses.

Before / After

Before: the generated title replaces "Untitled session"/"New session" in a single frame. (And in the original pre-#40318 wipe: a hard splice — full-brightness new characters cut against full-brightness old ones, firing on every title change.)

After: the wipe fires only on the placeholder → real transition — the background generated-title moment. The outgoing title dims toward the background the moment the wipe starts, the new title reveals left-to-right behind a 3-cell feathered edge (freshly revealed characters brighten as the front passes), and the front decelerates on an ease-out cubic over 450 ms. Every other title change — user renames, persisted-title sync corrections, real → real updates — jumps immediately, which is what #40318 was fixing.

How

packages/tui/src/component/session-tabs.tsx — createTitleWipe, shared by both orientations:

• Keeps the outgoing title and tweens a front cut 0 → 1 (tween with ease-out cubic, 0.45 s). The gate lives in its effect: any transition that is not placeholder → real jumps to front: 1 with no outgoing title retained.
• parts splices incoming graphemes over outgoing ones per cell (padded with spaces where lengths differ, so a shorter incoming title erases the tail as the front passes).
• mix(index) returns a per-cell tint toward the background: the outgoing block sits at ~50% dim (deepening slightly as the wipe advances, with a fast ramp-in so the start doesn't flash), and the WIPE_FEATHER cells behind the front ramp freshly revealed characters from dim to full.
• Both layouts feed their existing visible-parts memos through the helper; characterColor/titleColor apply mix after the existing glow and fade treatments, and the per-character render path is forced while a wipe is active.

Flow

flowchart LR
    change["tab.title changes"] --> gate{"previous title was\na placeholder?"}
    gate -->|no| jump["jump: render new title immediately"]
    gate -->|yes| wipe["wipe: outgoing dims,\nfront reveals with feathered edge"]
    wipe --> settle["450ms ease-out → settled title"]

Scope

• No change to when titles update — only how the one placeholder → real transition renders.
• The tab strip cannot distinguish a user rename from a generated title (session.renamed carries no source), so the gate is prior-state based; a user manually titling an untitled session also wipes, which reads fine.

Testing

• bun typecheck (packages/tui) clean.
• bun run test (packages/tui): 647 tests, 0 fail.
• Verified live in a real PTY via terminal-control in both orientations: captured mid-wipe frames show the bright incoming prefix, the feathered edge, and the uniformly dimmed outgoing remainder ("Queitled session"); a failed first run keeps the placeholder without firing the wipe.

Demo

Storybook (OPENCODE_STORY=session-tabs), vertical rail: two tabs open untitled (dim, italic — from #41921) and earn their titles on their first completed run, each wiping in with the dimmed-outgoing, feathered-edge treatment.