fix(terminal): remote and Docker tabs keep the byte tail on a switch (#588 merge-time fix)

A remote (ssh) or Docker session's local pane hosts a nested tmux client in
the alternate screen, so it always reports paneHistoryLines 0 while its byte
tail carries the real scrolled-off output. The new full=1 switch therefore
replaced their scrollback with the visible frame on every revisit. Those
sessions now keep the tail; the pinned test string and the invariants note
say so.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -213,7 +213,7 @@ Further detail: the `<prefix>: <title>` form (`w3-myapp: fix the login redirect`
 
 **The partial-history notice is lazy and pane-gated** (`computeHistoryTruncationNotice()` in constants.js, `_renderHistoryTruncationBanner()` / `_setHistoryNoticeRevealed()` in app.js). `truncated` on a terminal response measures the server's BYTE stream, which is not what `full=1` can return: for a pane with no tmux scrollback (fullscreen claude starts in the alternate screen and never writes to the main grid, so `#{history_size}` is 0) the bytes a tail cut drops are old repaint frames. Measured on prod 2026-10-10, every claude pane: the tab-switch tail cut a 1.2 to 6.2 MB stream to 1 MiB, the local scrollback that tail replays into is repeats of the same frames (one pane: 450 non-blank rows, 44 unique, one row 33 times), and `full=1` returned 1 to 5 KB, so **Load full history** could only end in the downgrade refusal while the banner promised "4.8 MB more". The capture therefore reads `#{history_size}` in the SAME `display-message` as the cursor (no extra tmux call), the route returns it as `paneHistoryLines` (absent when the body is not a capture), and a reported 0 hides the notice in every state; a positive count replaces the byte gap in the message. ⚠️ Key the decision on `history_size`, never on `alternate_on`: a shell running `less` is in the alternate screen with its whole history still retained (measured, 99,972 rows) and `full=1` returns all of it. The notice is also LAZY: it appears only after a wheel/touch gesture reaches the top of the browser buffer and the pull that gesture started has settled (`_maybeLoadMoreHistoryOnScroll`), goes away when a downward gesture is back at live output or the tab switches (`selectSession` nulls `_historyNoticeRevealedFor` before repainting), and its × is sticky per session until reload (`_historyNoticeDismissed`). Tests: `test/history-truncation-notice.test.ts`, `test/history-notice-reveal.test.ts`.
 
-**A tab switch to a pane with no tmux scrollback takes `full=1`, not the 1 MiB tail** (`_paneHistoryLines` + `_notePaneHistory()` in app.js). Every terminal response (select, refresh, re-pull) records `paneHistoryLines` per session, and `selectSession` serves a non-shell switch from `full=1` whenever the last report was 0. For such a pane that capture IS the visible frame (0.9 to 5.6 KB on prod) and matches what a page load shows, while the tail was 1 MiB of old repaints. Measured 2026-10-10 with real prod payloads through the real client in chromium: median switch 1.26 to 1.66 s down to 0.10 to 0.19 s, parse ~1.1 to 1.5 s down to 2 to 3 ms; server time 136 to 1070 ms (tail) vs 89 to 330 ms (full). An empty local buffer is also what lets `_maybePageCliTranscript` send a gesture to the CLI's own transcript. ⚠️ Only a reported 0 counts: a response without the field FORGETS the entry (unknown is never empty), so an older server or a byte-history fallback keeps the tail; a pane that starts keeping history (claude switched to its inline view) is learned from the next response and goes back to the tail. ⚠️ Shells never take this path. ⚠️ The refresh path (`_onSessionNeedsRefresh`) keeps its downgrade guard unchanged: a server-triggered refresh must not wipe local rows the user may be reading. Tests: `test/pane-history-memory.test.ts`, `test/fullscreen-tab-switch-capture.browser.test.ts` (browser suite).
+**A tab switch to a pane with no tmux scrollback takes `full=1`, not the 1 MiB tail** (`_paneHistoryLines` + `_notePaneHistory()` in app.js). Every terminal response (select, refresh, re-pull) records `paneHistoryLines` per session, and `selectSession` serves a non-shell switch from `full=1` whenever the last report was 0. For such a pane that capture IS the visible frame (0.9 to 5.6 KB on prod) and matches what a page load shows, while the tail was 1 MiB of old repaints. Measured 2026-10-10 with real prod payloads through the real client in chromium: median switch 1.26 to 1.66 s down to 0.10 to 0.19 s, parse ~1.1 to 1.5 s down to 2 to 3 ms; server time 136 to 1070 ms (tail) vs 89 to 330 ms (full). An empty local buffer is also what lets `_maybePageCliTranscript` send a gesture to the CLI's own transcript. ⚠️ Only a reported 0 counts: a response without the field FORGETS the entry (unknown is never empty), so an older server or a byte-history fallback keeps the tail; a pane that starts keeping history (claude switched to its inline view) is learned from the next response and goes back to the tail. ⚠️ Shells never take this path. ⚠️ Remote and Docker sessions never take this path: their local pane hosts a nested tmux client in the alternate screen, so it reports 0 while the byte tail carries the real scrolled-off output. ⚠️ The refresh path (`_onSessionNeedsRefresh`) keeps its downgrade guard unchanged: a server-triggered refresh must not wipe local rows the user may be reading. Tests: `test/pane-history-memory.test.ts`, `test/fullscreen-tab-switch-capture.browser.test.ts` (browser suite).
 
 **A capture reports the geometry it was taken at** (#435): a visible frame repaints each row at an absolute position, counting up to the pane's height and out to the pane's width, so a terminal smaller than that pane damages it two ways at once. Too short and every address past the browser's own height clamps onto the last line, overwriting the rows underneath (measured: against a 50-row pane, a 30-row terminal rendered 28 of a 45-line command and drew the survivors twice). Too narrow and each row is painted out to the pane's width, so the browser wraps every painted row and the wrap on the last one scrolls the whole frame up by one. Nothing in the response used to say what geometry the frame was built for, so the client could not see either case. `PaneCaptureOptions.capturedGeometry` carries it out, and the terminal response publishes it as `captureCols`/`captureRows`. ⚠️ **Both fields are ABSENT unless a frame was really positioned**, and every consumer must test `Number.isFinite` rather than truthiness: `mux-visible` is necessary but not sufficient, because when the `display-message` cursor query fails `capturePaneBuffer` skips the snapshot repaint and returns the raw capture, and the route still labels that non-empty body `mux-visible`. A body that positioned nothing has no geometry to describe and nothing to repair, so a comparison that fires there buys a second capture, a reset plus chunked rewrite, a dropped and reopened WebSocket and a discarded xterm snapshot for no gain. ⚠️ **The comparison runs on `mux-visible` ONLY.** A full-history body is linear scrollback closed by a RELATIVE cursor move, which is relative precisely so the browser's row count need not match the pane's, and a byte-history body carries no row alignment at all, so a size mismatch damages neither and a replay repairs neither. That gate matters because the first select of every non-shell session per page takes the full-history path, where an ungated comparison would fire most often on the one response it cannot help, at the price of a second whole-scrollback capture. ⚠️ **The replay is capped at one attempt and latches per session when it cannot converge.** `resizeRetry` stops two competing fits trading replays forever; a pane already drawing at the size just requested is left alone, because a retry would capture the identical frame; and a pass that still does not converge joins `_geometryRetryUseless`, so the case `Session.resize` declines outright (a small viewport while a desktop viewport's size claim is live, where the retry re-sends the same declined resize and captures the same pane) costs one attempt per session per page load instead of one per select. ⚠️ **The clamp used to manufacture that equality, and no longer can** (#464). This paragraph previously explained it as the signature of a clamp: `getTerminalDimensions()` floors at 40x10 while `fitAddon.fit()` did not, so a terminal under 40 columns or 10 rows reported a pane permanently bigger than itself and would replay on every tab switch. That divergence is fixed at the source — `syncTerminalGeometry()` (terminal-ui.js) fits, floors and APPLIES in one step, so the browser terminal IS the size it reports. The only remaining reason the two can differ is a resize the server declined, which the server now reports back (`Session.ptyGeometry`, the `{"t":"zc"}` frame and the resize response) for the client to adopt by COLUMNS. The equality guard stays, for the plain case of a pane already at the requested size. ⚠️ **A retry pass must not re-arm `_fullHistoryLoaded`**: it did not consume the full-history pull, and re-arming it would spend a whole-scrollback capture on the next select. That branch is currently unreachable by construction, since reaching it needs `source === 'mux-visible'` while a `full=1` pass is answered `mux-full-history` or `history`; a static test over the source is the habit this repo uses for an invariant nothing can execute. Tests: `test/capture-geometry-retry.browser.test.ts` (eight cases, five of which fail against the merge base), `test/tmux-capture-full-history.test.ts`, `test/routes/session-routes.test.ts`.
 

src/web/public/app.js

@@ -9394,7 +9394,10 @@ class CodemanApp {
       // response re-reports the count, so a pane that starts keeping history
       // (claude switched to its inline view) goes back to the tail on the next
       // switch.
-      const paneKeepsNoHistory = this._paneHistoryLines?.get(sessionId) === 0;
+      // A remote (ssh) or Docker session's local pane hosts a nested tmux client in the
+      // alternate screen, so it reports 0 while its byte tail is real scrollback.
+      const paneKeepsNoHistory =
+        !session?.remote && !session?.docker && this._paneHistoryLines?.get(sessionId) === 0;
       const useFullHistory =
         session?.mode !== 'shell' && (paneKeepsNoHistory || !this._fullHistoryLoaded.has(sessionId));
       if (useFullHistory) this._fullHistoryLoaded.add(sessionId);

test/history-truncation-notice.test.ts

@@ -194,7 +194,7 @@ describe('the in-terminal truncation line is gone (static guard)', () => {
     expect(app).toContain(
       "session?.mode !== 'shell' && (paneKeepsNoHistory || !this._fullHistoryLoaded.has(sessionId))"
     );
-    expect(app).toContain('const paneKeepsNoHistory = this._paneHistoryLines?.get(sessionId) === 0;');
+    expect(app).toContain('!session?.remote && !session?.docker && this._paneHistoryLines?.get(sessionId) === 0;');
     expect(app).toContain("!restoredSnapshot && session?.mode !== 'shell'");
     expect(app).toContain('`/api/sessions/${sessionId}/terminal?tail=${TERMINAL_TAIL_SIZE}`');
     // Every terminal capture now goes through _fetchTerminalCapture, which adds