Merge pull request #331 from dignfei/fix/shell-history-performance

fix(terminal): bound shell history replay

docs/architecture-invariants.md

@@ -92,7 +92,7 @@ Implementation detail extracted from `CLAUDE.md` so that file stays small enough
 
 ### Full-scrollback replay
 
-**Full-scrollback replay** (COD-164/#148, reworked for #205): `GET /api/sessions/:id/terminal?full=1` returns the ENTIRE tmux scrollback (capture-pane `-e -S -<lines>` bounded by the configured history limit, explicit `maxBuffer` from the terminal-history config, early byte-cap before normalization, CRLF-normalized for shell panes). On success the capture is returned ALONE (`source='mux-full-history'` — it supersedes the byte buffer; no duplication). The first load OF EACH SESSION per page load requests `full=1` (`_fullHistoryLoaded` Set in app.js — the old one-shot `_initialFullBufferLoad` flag was consumed by whichever tab auto-selected, leaving every other tab one frame of history); later switches keep the cheap `?tail=` visible-frame path. On top of that, scrolling up while already at the TOP of the buffer re-pulls `full=1` on demand (`_maybeRefetchFullHistory`, 4s per-session cooldown, in-flight + tab-switch guards, viewport position held across the replay). The re-pull exists because xterm's buffer is only a WINDOW onto tmux's history and two things shrink it: tmux coalesces bursty output into pane REPAINTS that overwrite rows instead of emitting linefeeds (measured: a 60-line burst added 1 row of browser scrollback and destroyed 34), and a tab switch replays only the visible frame. tmux's own history is intact throughout — the browser just has to ask for it again. On-demand rather than automatic because at a 100k history limit the capture can be megabytes. ⚠️ **The re-pull must never DOWNGRADE the buffer** (#205 round 2): the same reasoning that makes it a win for a shell pane makes it destructive for a repaint-mode CLI pane, where tmux keeps no history of its own (`history_size≈0` measured for a Claude pane) and the capture is roughly ONE frame while xterm may hold hundreds of rows of replayed frames — `_resetTerminalForReplay()` + rewrite then deletes history mid-scroll ("goes back a bit, repeats blocks, gets worse the further up I go"; measured A/B on a live pane: 341 rows → 42 with the guard off). `_replayWouldShrinkBuffer()` (terminal-ui.js) estimates the capture's rendered rows — escape sequences stripped, `capture-pane -J` re-wrapping accounted for — and the pull is skipped when that is more than one screen short of `buffer.active.length`. The one-screen tolerance matters: both sides are estimates (the buffer length counts trailing blank rows), so only a clear downgrade is refused. A refused session joins `_fullHistoryRepullUseless`, raising its cooldown from 4s to 60s so a hollow pane stops re-fetching megabytes on every scroll-up. Tests: `test/tmux-capture-full-history.test.ts`, `test/tmux-scrollback-eol.test.ts`, `test/terminal-scroll-routing.test.ts`.
+**Full-scrollback replay** (COD-164/#148, reworked for #205): `GET /api/sessions/:id/terminal?full=1` returns the ENTIRE tmux scrollback (capture-pane `-e -S -<lines>` bounded by the configured history limit, explicit `maxBuffer` from the terminal-history config, early byte-cap before normalization, CRLF-normalized for shell panes). On success the capture is returned ALONE (`source='mux-full-history'` — it supersedes the byte buffer; no duplication). The first load of each non-shell TUI session per page requests `full=1` (`_fullHistoryLoaded` Set in app.js — the old one-shot `_initialFullBufferLoad` flag was consumed by whichever tab auto-selected, leaving every other TUI tab one frame of history). Shell sessions instead load a bounded 1 MiB `?tail=` window on every selection: a 100k-line shell capture can be tens of MiB, and automatically parsing it makes tab-switch latency scale with the entire session. Shell full history is therefore explicit-button-only; reaching the top during an ordinary wheel/touch gesture must not reset xterm and replay the multi-megabyte capture on its main thread. Other modes may still re-pull `full=1` at the TOP, and pressing **Load full history** forces the request for any recoverably truncated session (`_maybeRefetchFullHistory`, 4s per-session gesture cooldown, in-flight + tab-switch guards, viewport position held across the replay); Shell full pulls are not retained in the tab cache, so the next switch stays bounded. Chunked replay enqueues 32 KiB pieces across safe yields, appends an xterm parse marker, then releases the live-output gate; output arriving after that release stays ordered behind the snapshot, while the marker callback supplies accurate parse timing without extending the pre-existing queued-event discard window. The route exposes capture/prepare totals in `Server-Timing`, while `[TERMINAL-PERF]` separates TTFB, body/JSON, reset+parse and total time for both selection and on-demand full pulls; parse completion is not a browser compositor/GPU paint measurement. The re-pull exists because xterm's buffer is only a WINDOW onto tmux's history and two things shrink it: tmux coalesces bursty output into pane REPAINTS that overwrite rows instead of emitting linefeeds (measured: a 60-line burst added 1 row of browser scrollback and destroyed 34), and a tab switch replays only the visible frame. tmux's own history is intact throughout — the browser just has to ask for it again. On-demand rather than automatic because at a 100k history limit the capture can be megabytes. ⚠️ **The re-pull must never DOWNGRADE the buffer** (#205 round 2): the same reasoning that makes it a win for a shell pane makes it destructive for a repaint-mode CLI pane, where tmux keeps no history of its own (`history_size≈0` measured for a Claude pane) and the capture is roughly ONE frame while xterm may hold hundreds of rows of replayed frames — `_resetTerminalForReplay()` + rewrite then deletes history mid-scroll ("goes back a bit, repeats blocks, gets worse the further up I go"; measured A/B on a live pane: 341 rows → 42 with the guard off). `_replayWouldShrinkBuffer()` (terminal-ui.js) estimates the capture's rendered rows — escape sequences stripped, `capture-pane -J` re-wrapping accounted for — and the pull is skipped when that is more than one screen short of `buffer.active.length`. The one-screen tolerance matters: both sides are estimates (the buffer length counts trailing blank rows), so only a clear downgrade is refused. A refused session joins `_fullHistoryRepullUseless`, raising its cooldown from 4s to 60s so a hollow pane stops re-fetching megabytes on every scroll-up. Tests: `test/tmux-capture-full-history.test.ts`, `test/tmux-scrollback-eol.test.ts`, `test/terminal-scroll-routing.test.ts`.
 
 ### Terminal scrollback: strip flavors and wheel/touch forwarding
 
@@ -377,7 +377,7 @@ Anatomy: `.set-shell` → `.set-shell-head` (title + `.set-head-actions`) + `.se
 
 ### Buffers, uploads, and terminal history
 
-Target: 20 sessions, 50 agent windows at 60fps. Limits in `src/config/`: terminal 32MB (see below), text 1MB, messages 1000, max agents 500, max sessions 50, max SSE clients 100. **Terminal history** (`src/config/terminal-history.ts`, COD-80): tmux history-limit 100k lines, PTY buffer 32MB max / 24MB trim (env `CODEMAN_MAX_TERMINAL_BUFFER`/`CODEMAN_TRIM_TERMINAL_TO`; the env-derived trim is clamped ≤75% of max — trim ≥ max would disable `BufferAccumulator` trimming entirely = unbounded memory); browser xterm scrollback stays a separate hardcoded 50k (`DEFAULT_SCROLLBACK` in constants.js — 100k/tab is a mobile-memory hazard). Settings keys `terminalScrollbackLines`/`terminalBufferMaxBytes`/`terminalBufferTrimBytes` are schema-validated but inert (only `tmuxHistoryLimit` is wired live); `buffer-limits.ts` re-exports the defaults. Text/message limits are env-overridable too (`CODEMAN_MAX_TEXT_OUTPUT`/`CODEMAN_TRIM_TEXT_TO`/`CODEMAN_MAX_MESSAGES`). **Image upload** (`image-input.js` / `config/buffer-limits.ts`): up to `_maxBatchImages` 20 images/batch (bounded concurrency 3), per-file `MAX_PASTE_IMAGE_BYTES` 50MB (env `CODEMAN_MAX_PASTE_IMAGE_BYTES`); the mobile camera-roll picker auto-downscales to fit before upload. **HEIC paste uploads** (#151): converted server-side to JPEG in a `worker_threads` worker (`web/heic-jpeg-worker.ts`, resourceLimits + 30s timeout) gated by `runWithConversionLimit()`; detection is magic-byte based (covers Android/MIUI HEIFs mislabeled as JPEG); headers declaring > 64MP are rejected 415 BEFORE decode (decompression-bomb guard). Deps: `heic-decode` + `jpeg-js`. Use `LRUMap` for bounded caches, `StaleExpirationMap` for TTL cleanup. Anti-flicker pipeline: `docs/terminal-anti-flicker.md`.
+Target: 20 sessions, 50 agent windows at 60fps. Limits in `src/config/`: terminal 32MB (see below), text 1MB, messages 1000, max agents 500, max sessions 50, max SSE clients 100. **Terminal history** (`src/config/terminal-history.ts`, COD-80): tmux history-limit 100k lines, PTY buffer 32MB max / 24MB trim (env `CODEMAN_MAX_TERMINAL_BUFFER`/`CODEMAN_TRIM_TERMINAL_TO`; the env-derived trim is clamped ≤75% of max — trim ≥ max would disable `BufferAccumulator` trimming entirely = unbounded memory); browser xterm scrollback stays a separate hardcoded 50k (`DEFAULT_SCROLLBACK` in constants.js — 100k/tab is a mobile-memory hazard). tmux <3.7 allocates history at pane creation, so `createSession()` sets the global default in the same command queue immediately before `new-session`; tmux 3.7+ instead creates the session and targets only that pane, because changing the global option can resize and trim unrelated live panes. A settings change resizes tracked panes only on 3.7+ and otherwise affects future panes; no version can recover lines already evicted. Settings keys `terminalScrollbackLines`/`terminalBufferMaxBytes`/`terminalBufferTrimBytes` are schema-validated but inert (only `tmuxHistoryLimit` is wired); `buffer-limits.ts` re-exports the defaults. Text/message limits are env-overridable too (`CODEMAN_MAX_TEXT_OUTPUT`/`CODEMAN_TRIM_TEXT_TO`/`CODEMAN_MAX_MESSAGES`). **Image upload** (`image-input.js` / `config/buffer-limits.ts`): up to `_maxBatchImages` 20 images/batch (bounded concurrency 3), per-file `MAX_PASTE_IMAGE_BYTES` 50MB (env `CODEMAN_MAX_PASTE_IMAGE_BYTES`); the mobile camera-roll picker auto-downscales to fit before upload. **HEIC paste uploads** (#151): converted server-side to JPEG in a `worker_threads` worker (`web/heic-jpeg-worker.ts`, resourceLimits + 30s timeout) gated by `runWithConversionLimit()`; detection is magic-byte based (covers Android/MIUI HEIFs mislabeled as JPEG); headers declaring > 64MP are rejected 415 BEFORE decode (decompression-bomb guard). Deps: `heic-decode` + `jpeg-js`. Use `LRUMap` for bounded caches, `StaleExpirationMap` for TTL cleanup. Anti-flicker pipeline: `docs/terminal-anti-flicker.md`.
 
 ## Local packages and build artifacts
 

docs/wiki/The-Dashboard.md

@@ -133,8 +133,10 @@ TUIs render correctly.
 
 Worth knowing:
 
-- **Scrollback.** The first time you open a session, Codeman pulls the entire tmux
-  scrollback, not just the recent tail. Scrolling to the very top pulls again on demand.
+- **Scrollback.** Agent/TUI sessions pull their entire tmux scrollback on first open.
+  Shell sessions open from a bounded recent tail so a large transcript cannot stall tab
+  switching; press **Load full history** to pull the rest explicitly. Ordinary Shell scrolling
+  stays within the bounded browser buffer so dragging upward remains responsive.
 - **Wheel and touch scrolling** are forwarded into Claude's own transcript on recent Claude
   versions, so the wheel scrolls the conversation rather than the terminal. `Shift+Wheel` is
   always local scrollback. Other CLIs scroll locally.