Add native tmux control mode and HTM integration

.github/actions/spelling/expect/expect.txt

@@ -323,6 +323,7 @@ CYSIZEFRAME
 CYSMICON
 CYVIRTUALSCREEN
 CYVSCROLL
+daemonizes
 dai
 DATABLOCK
 dbcs
@@ -750,7 +751,9 @@ HTCAPTION
 HTCLIENT
 HTLEFT
 HTMAXBUTTON
+htmd
 HTMINBUTTON
+htmtst
 HTRIGHT
 HTTOP
 HTTOPLEFT
@@ -1313,6 +1316,7 @@ PREVIEWWINDOW
 PREVLINE
 prg
 PRIs
+PROCESSENTRY
 processhost
 PROCESSINFOCLASS
 PRODEXT
@@ -1570,6 +1574,7 @@ SMARTQUOTE
 SMTO
 snapcx
 snapcy
+SNAPPROCESS
 snk
 SOLIDBOX
 Solutiondir
@@ -1696,6 +1701,7 @@ tmultiple
 tofrom
 Tombstoning
 toolbars
+Toolhelp
 TOOLINFO
 TOOLWINDOW
 TOPDOWNDIB
@@ -1851,13 +1857,15 @@ WCIA
 WCIW
 wcs
 WCSHELPER
+wcsicmp
 wcsrev
 wcswidth
 WCT
 wddm
 wddmcon
 WDDMCONSOLECONTEXT
 wdm
+wdupenv
 wekyb
 wex
 wextest

doc/specs/htm-integration.md

@@ -0,0 +1,139 @@
+---
+author: MisterTea
+created on: 2026-08-30
+last updated: 2026-08-30
+issue id: n/a
+---
+
+# HTM (headless terminal multiplexer) integration
+
+## Abstract
+
+This spec describes how Windows Terminal detects an EternalTerminal `htm` session on an existing ConPTY connection, takes over tabs/panes so they map onto `htmd`, and tears the session down without a new `connectionType`. The work is gated by `Feature_HtmIntegration` (enabled in Dev, disabled in Release and WindowsInbox).
+
+## Inspiration
+
+[hyper-htm](https://github.com/MisterTea/hyper-htm) wraps Hyper so that running `htm` in a tab steals that PTY, creates follower panes with no local PTY, and maps split/new-tab/close onto the `htmd` daemon. Windows Terminal has no Hyper-style plugin API: JSON fragments can inject profiles and color schemes only. Shell integration (OSC 133) and `ShellExtension` do not intercept splits. Matching that UX requires TerminalApp to wrap ConPTY, the same pattern as `DebugTapConnection`.
+
+EternalTerminal `htm`/`htmd` on Windows uses ConPTY for pane shells and AF_UNIX IPC at `%TEMP%\htm.<user>.ipc`. The wire protocol is unchanged so hyper-htm and Windows Terminal stay compatible.
+
+## Solution Design
+
+```
+  Windows Terminal                          EternalTerminal
+  ┌─────────────────────────────┐           ┌──────────────────────┐
+  │ Leader pane                 │  PTY      │ htm.exe byte bridge  │
+  │   ConPTY + HtmLeaderConnection ────────►│         │            │
+  │ Follower panes              │  framed   │         ▼ AF_UNIX    │
+  │   HtmFollowerConnection     │  packets  │ htmd.exe mux daemon  │
+  │ HtmSession (per window)     │           │   ConPTY per pane    │
+  └─────────────────────────────┘           └──────────────────────┘
+```
+
+### Why wrap ConPTY instead of a new `connectionType`
+
+Users type `htm` in an existing profile (PowerShell, cmd, WSL). A dedicated `connectionType` would require a separate profile and would not take over a tab that is already running. Wrapping every ConPTY in `HtmLeaderConnection` (behind the feature flag) matches Hyper: pass-through until `ESC[###q`, then consume framed packets.
+
+### Wire protocol
+
+Compatible with EternalTerminal `HtmHeaderCodes.hpp` and `hyper-htm/htm-core.js`.
+
+- Init: `ESC[###q` (pass through bytes before this; hold a partial match across chunks)
+- Exit: `ESC[$$$q` (leave HTM mode; leader shows a normal shell again)
+- Frame: `[1-byte header][8-char base64 of little-endian int32 length][payload]`
+- `SESSION_END` (`D`) is a single byte with no length field
+
+| Header | Payload | Direction |
+|--------|---------|-----------|
+| `1` INSERT_KEYS | 36-char pane UUID + base64 UTF-8 keys | client → server |
+| `2` INIT_STATE | JSON multiplexer state | server → client |
+| `3` CLIENT_CLOSE_PANE | pane UUID | client → server |
+| `4` APPEND_TO_PANE | pane UUID + base64 output | server → client |
+| `5` NEW_TAB | tab UUID + pane UUID | client → server |
+| `8` SERVER_CLOSE_PANE | pane UUID | server → client |
+| `9` NEW_SPLIT | source UUID + pane UUID + `'1'` vertical / `'0'` horizontal | client → server |
+| `A` RESIZE_PANE | base64 int32 cols + base64 int32 rows + pane UUID | client → server |
+| `B` DEBUG_LOG | base64 text | server → client |
+| `C` INSERT_DEBUG_KEYS | raw keys (leader keystrokes, Escape disconnect) | client → server |
+| `D` SESSION_END | none | either |
+
+UUIDs are 36-character `GuidToPlainString` values (no braces). HTM `'1'` is a vertical divider (Windows Terminal left/right); `'0'` is horizontal (up/down).
+
+### Types (`src/cascadia/TerminalApp/`)
+
+| Type | Role |
+|------|------|
+| `HtmProtocol` | Framing, CSI consume, packet parse |
+| `HtmLeaderConnection` | Wraps ConPTY; pass-through until init CSI; then consume packets and route leader keys as `INSERT_DEBUG_KEYS` |
+| `HtmFollowerConnection` | No process. `WriteInput` → `INSERT_KEYS`; `Resize` → `RESIZE_PANE`; `Close` → `CLIENT_CLOSE_PANE` |
+| `HtmSession` | Per-window on `TerminalPage`: UUID map, INIT_STATE layout, user split/tab intercept |
+
+On `INIT_STATE`, the first pane of the first tab maps onto the existing leader (no second ConPTY). Remaining panes are created with `HtmFollowerConnection` via sequential binary splits (HTM n-way splits). `APPEND_TO_PANE` / `DEBUG_LOG` are injected into the mapped `TermControl`s.
+
+While a session is active, split and new-tab on an HTM pane create a follower and send `NEW_SPLIT` / `NEW_TAB` instead of spawning ConPTY. Closing a follower sends `CLIENT_CLOSE_PANE`. Closing the leader or seeing `SESSION_END` / `ESC[$$$q` tears down followers and returns the leader to a normal shell; the Windows Terminal window stays open (Hyper closes the window; Windows Terminal only ends the HTM session).
+
+### Settings
+
+Put `htm.exe` / `htmd.exe` on `PATH`, or set a profile environment variable so a local EternalTerminal build is found:
+
+```json
+{
+    "profiles": {
+        "defaults": {
+            "environment": {
+                "HTM_BIN_DIR": "C:\\path\\to\\et\\build"
+            }
+        }
+    }
+}
+```
+
+When `HTM_BIN_DIR` is set, Terminal prepends it to `PATH` for that ConPTY. An optional profile `"commandline": "htm.exe"` is not required for takeover.
+
+## UI/UX Design
+
+1. Open Windows Terminal, run `htm` in any ConPTY profile.
+2. Extra panes/tabs appear matching the multiplexer state (including restored scrollback).
+3. Typing in a follower is injected into `htmd`; output streams back as `APPEND_TO_PANE`.
+4. Split / new tab from an HTM pane create remote panes, not local shells.
+5. Escape (via `htm` debug keys) or `ESC[$$$q` leaves HTM mode; `htm` again restores the session.
+
+## Capabilities
+
+### Accessibility
+
+Follower panes are normal `TermControl` instances. Screen readers see the same text buffer as any other pane. No new UI chrome.
+
+### Security
+
+`htm`/`htmd` already run as the current user. AF_UNIX IPC is per-user under `%TEMP%`. This feature only interprets bytes already produced by a user-started process. `HTM_BIN_DIR` is an explicit profile setting.
+
+### Reliability
+
+Malformed frames drop HTM mode instead of wedging the connection. Leader close disconnects the session without closing the whole window. Unknown HTM headers cause `htmd` to disconnect that client.
+
+### Compatibility
+
+Disabled in Release and WindowsInbox via `Feature_HtmIntegration`. Dev builds wrap ConPTY; until `htm` prints `ESC[###q`, behavior is unchanged. The wire protocol is not versioned independently of EternalTerminal / hyper-htm.
+
+### Performance, Power, and Efficiency
+
+Pass-through copies ConPTY output until init. After takeover, framed packets replace raw PTY traffic for followers (no extra processes). Overhead is comparable to `DebugTapConnection`.
+
+## Potential Issues
+
+- This environment cannot compile Windows Terminal; first verification needs Windows 10 2004+ and Visual Studio.
+- JSON fragment extensions cannot provide this behavior; an upstream plugin API (GH#4000) would be a larger design.
+- Undo-close of an HTM follower may recreate a local ConPTY instead of a follower.
+- n-way HTM splits are approximated with sequential 50/50 binary splits.
+
+## Future considerations
+
+A first-class `connectionType` or connection-wrapper extension point would let this live out-of-tree. Until then, a feature-flagged branch is the reviewable shape for an upstream PR.
+
+## Resources
+
+- EternalTerminal `src/htm/` (`HtmHeaderCodes.hpp`, `HtmClient`, `HtmServer`, `TerminalHandler`)
+- [hyper-htm](https://github.com/MisterTea/hyper-htm) `htm-core.js`, `index.js`
+- `DebugTapConnection` in TerminalApp
+- Windows Terminal GH#4000 (extensibility)

src/cascadia/TerminalApp/AppActionHandlers.cpp

@@ -29,8 +29,8 @@ namespace winrt
     using IInspectable = Windows::Foundation::IInspectable;
 }
 
-namespace winrt::TerminalApp::implementation
-{
+namespace winrt::TerminalApp::implementation
+{
     TermControl TerminalPage::_senderOrActiveControl(const IInspectable& sender)
     {
         if (sender)
@@ -265,9 +265,9 @@ namespace winrt::TerminalApp::implementation
         return false;
     }
 
-    void TerminalPage::_HandleSplitPane(const IInspectable& sender,
-                                        const ActionEventArgs& args)
-    {
+    void TerminalPage::_HandleSplitPane(const IInspectable& sender,
+                                        const ActionEventArgs& args)
+    {
         if (args == nullptr)
         {
             args.Handled(false);
@@ -284,6 +284,26 @@ namespace winrt::TerminalApp::implementation
 
             const auto& activeTab{ _senderOrFocusedTab(sender) };
 
+            if (Feature_HtmIntegration::IsEnabled() && _htmSession && _htmSession->IsActive())
+            {
+                const auto focusedConn = _HtmFocusedConnection();
+                const auto sourceId = _HtmPaneIdFromConnection(focusedConn);
+                if (!sourceId.empty())
+                {
+                    const auto direction = realArgs.SplitDirection();
+                    const bool vertical = direction != SplitDirection::Up && direction != SplitDirection::Down;
+                    if (const auto follower{ _htmSession->CreateFollowerForUserSplit(sourceId, vertical) })
+                    {
+                        _SplitPane(activeTab,
+                                   direction,
+                                   realArgs.SplitSize(),
+                                   _MakePane(realArgs.ContentArgs(), duplicateFromTab, follower));
+                        args.Handled(true);
+                        return;
+                    }
+                }
+            }
+
             _SplitPane(activeTab,
                        realArgs.SplitDirection(),
                        // This is safe, we're already filtering so the value is (0, 1)
@@ -456,23 +476,38 @@ namespace winrt::TerminalApp::implementation
         args.Handled(true);
     }
 
-    void TerminalPage::_HandleNewTab(const IInspectable& /*sender*/,
-                                     const ActionEventArgs& args)
-    {
-        if (args == nullptr)
-        {
-            LOG_IF_FAILED(_OpenNewTab(nullptr));
-            args.Handled(true);
-        }
-        else if (const auto& realArgs = args.ActionArgs().try_as<NewTabArgs>())
+    void TerminalPage::_HandleNewTab(const IInspectable& /*sender*/,
+                                     const ActionEventArgs& args)
+    {
+        const auto realArgs = args ? args.ActionArgs().try_as<NewTabArgs>() : nullptr;
+        if (Feature_HtmIntegration::IsEnabled() && _htmSession && _htmSession->IsActive())
+        {
+            const auto focusedConn = _HtmFocusedConnection();
+            if (!_HtmPaneIdFromConnection(focusedConn).empty())
+            {
+                if (const auto follower{ _htmSession->CreateFollowerForUserTab() })
+                {
+                    _CreateNewTabFromPane(_MakePane(realArgs ? realArgs.ContentArgs() : nullptr, nullptr, follower));
+                    args.Handled(true);
+                    return;
+                }
+            }
+        }
+
+        if (args == nullptr)
+        {
+            LOG_IF_FAILED(_OpenNewTab(nullptr));
+            return;
+        }
+        else if (realArgs)
         {
             if (_shouldBailForInvalidProfileIndex(_settings, realArgs.ContentArgs()))
             {
                 args.Handled(false);
                 return;
             }
 
-            LOG_IF_FAILED(_OpenNewTab(realArgs.ContentArgs()));
+            LOG_IF_FAILED(_OpenNewTab(realArgs.ContentArgs()));
             args.Handled(true);
         }
     }