COD-105 discover + attach existing remote tmux sessions (detach-not-kill)

Phase 2 of the remote-tmux arc. Discover codeman-* tmux sessions already
running on a remote host (created by the remote's own Codeman or another
instance) and attach to one this Codeman didn't launch, with detach-not-kill
ownership for non-owned sessions.

- remote-hosts.ts: listRemoteCodemanSessions (ssh, VITEST-guarded, never throws)
  + pure parseRemoteSessionList + buildRemoteListSessionsCommand. Parser splits
  on the LITERAL \t the remote tmux emits (next-3.7 does not expand \t) AND a
  real tab. toAttachedSessionRemote builds a non-owned SessionRemote; toSessionRemote
  now marks the COD-104 launch path owned:true.
- tmux-manager.ts: buildRemoteAttachCommand (sibling of buildRemoteLaunchCommand);
  buildRemoteSessionCommand selects attach vs launch by ownership. killSession gains
  a detach-not-kill early return for non-owned remote sessions: tears down only the
  LOCAL pane (kills local ssh -> remote attach detaches), NEVER issues a remote
  kill-session.
- types/session.ts: RemoteSessionInfo; SessionRemote.owned + remoteSessionName.
- schemas.ts: CreateSessionSchema.attachRemoteSession {hostId, remoteSessionName};
  fixed a pre-existing no-useless-escape lint error in the jumpHost regex.
- case-routes.ts: GET /api/remote-hosts/:hostId/sessions (explicit discovery).
- session-routes.ts: attachRemoteSession create path -> non-owned session.
- UI (index.html/session-ui.js/styles.css): explicit "Discover existing sessions"
  button + Attach action (owned:false). No auto-discover.

Verified on aa-desktop: discovered codeman-disco1, attached (attached=1, shared
view), killed local probe pane -> remote SURVIVED_DETACH (attached=0). Tests:
parse/attach-cmd/ownership unit + discovery route, session-routes + case-routes green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
(cherry picked from commit 55f5ada9db6d01518a4adf6b752e460b5df39524)

src/remote-hosts.ts

@@ -8,6 +8,7 @@ import type {
   RemoteCase,
   RemoteCommandMode,
   RemoteHost,
+  RemoteSessionInfo,
   RemoteSshOptions,
   SessionMode,
   SessionRemote,
@@ -210,6 +211,105 @@ export async function checkRemoteTmuxAvailable(
   }
 }
 
+/**
+ * COD-105 — build the SSH command that lists `codeman-*` tmux sessions on a
+ * remote host's canonical `-L codeman` socket.
+ *
+ * `list-sessions` exits NON-ZERO with empty output when no sessions exist (and
+ * the server isn't running), so `2>/dev/null` swallows tmux's "no server
+ * running" stderr; the caller treats a non-zero exit / empty output as "no
+ * sessions" rather than an error.
+ *
+ * COD-107 — connection options come from the shared `buildSshConnectionArgs`, so
+ * discovery connects with the SAME port/identity/proxy/jump-host as the launch
+ * and the tmux prereq probe.
+ */
+export function buildRemoteListSessionsCommand(
+  host: Pick<RemoteHost, 'username' | 'host' | 'port'> & RemoteSshOptions
+): string {
+  const [ssh, ...connectionArgs] = buildSshConnectionArgs(host);
+  const parts = [ssh, connectionArgs[0], '-o ConnectTimeout=10', ...connectionArgs.slice(1)];
+  // The tmux list-sessions invocation is passed as ONE shell-quoted argument so
+  // the remote login shell runs it verbatim. The `-F` format uses literal `\t`
+  // separators (tmux expands them); `2>/dev/null` is inside the quoted command.
+  const remoteCmd =
+    'tmux -L codeman list-sessions -F "#{session_name}\\t#{session_attached}\\t#{session_created}\\t#{session_windows}" 2>/dev/null';
+  parts.push(remoteSshTarget(host), shellescape(remoteCmd));
+  return parts.join(' ');
+}
+
+/**
+ * COD-105 — pure parser for the `tmux list-sessions -F` output emitted by
+ * `buildRemoteListSessionsCommand`. Factored out so the parse is unit-testable
+ * without opening a real ssh connection.
+ *
+ * - Splits each non-empty line into [name, attached, created, windows] on the
+ *   field separator. IMPORTANT: the remote tmux's `-F "…\t…"` format does NOT
+ *   expand `\t` to a real tab — it emits the LITERAL two-character sequence
+ *   `\t` (verified on aa-desktop / tmux next-3.7). So we split on the literal
+ *   backslash-t sequence; we also tolerate a real tab in case a tmux build
+ *   does expand it. (A real TAB is the regex `\t`; a literal backslash-t is the
+ *   regex `\\t`.)
+ * - Keeps ONLY sessions whose name starts with `codeman-` (ignores foreign tmux
+ *   sessions that happen to share the socket).
+ * - Coerces: `attached` → boolean (`'1'`), `created`/`windows` → finite ints.
+ * - Skips malformed lines (wrong column count or non-numeric created/windows)
+ *   rather than emitting garbage.
+ */
+export function parseRemoteSessionList(stdout: string): RemoteSessionInfo[] {
+  const out: RemoteSessionInfo[] = [];
+  for (const rawLine of stdout.split('\n')) {
+    const line = rawLine.trim();
+    if (!line) continue;
+    // Split on a literal `\t` (backslash + t, what the remote tmux emits) OR a
+    // real tab character. `/\\t|\t/` = the two-char sequence, or a TAB.
+    const cols = line.split(/\\t|\t/);
+    if (cols.length !== 4) continue;
+    const [name, attachedStr, createdStr, windowsStr] = cols;
+    if (!name.startsWith('codeman-')) continue;
+    const created = Number(createdStr);
+    const windows = Number(windowsStr);
+    if (!Number.isFinite(created) || !Number.isFinite(windows)) continue;
+    out.push({
+      name,
+      attached: attachedStr.trim() === '1',
+      created: Math.trunc(created),
+      windows: Math.trunc(windows),
+    });
+  }
+  return out;
+}
+
+/**
+ * COD-105 — discover `codeman-*` tmux sessions already running on a remote host
+ * (created by the remote's own Codeman, another instance, or this one), so the
+ * operator can attach to one this Codeman didn't launch.
+ *
+ * NEVER throws: returns `[]` on unreachable host / no tmux / no sessions
+ * (`list-sessions` exits non-zero with empty output when there are none).
+ *
+ * VITEST guard — like `checkRemoteTmuxAvailable`, returns `[]` under test so a
+ * real ssh never runs in a request path (which would make route tests hit a
+ * ~10s timeout). The command construction is covered by
+ * `buildRemoteListSessionsCommand` and the parse by `parseRemoteSessionList`.
+ */
+export async function listRemoteCodemanSessions(
+  remote: Pick<RemoteHost, 'username' | 'host' | 'port'> & RemoteSshOptions
+): Promise<RemoteSessionInfo[]> {
+  if (process.env.VITEST) {
+    return [];
+  }
+  const command = buildRemoteListSessionsCommand(remote);
+  try {
+    const { stdout } = await execAsync(command, { timeout: 15_000 });
+    return parseRemoteSessionList(stdout);
+  } catch {
+    // Unreachable host, no tmux server, or no sessions (non-zero exit). All map
+    // to "nothing to attach to" — never surface as an error to the caller.
+    return [];
+  }
+}
+
 export function remoteDisplayPath(
   remote: Pick<SessionRemote, 'username' | 'host' | 'remotePath'> | { username: string; host: string; path: string }
 ): string {
@@ -226,6 +326,10 @@ export function toSessionRemote(host: RemoteHost, remoteCase: RemoteCase): Sessi
     port: host.port,
     remotePath: remoteCase.remotePath,
     commands: host.commands,
+    // COD-105 — the COD-104 launch path creates the remote session, so we own it
+    // (an explicit kill may propagate a remote kill-session). Discovered+attached
+    // sessions go through `toAttachedSessionRemote` with `owned: false`.
+    owned: true,
     // COD-107 — carry the advanced SSH options from host config into the session
     // so the launch/prereq commands connect the same way the operator configured.
     identityFile: host.identityFile,
@@ -234,3 +338,38 @@ export function toSessionRemote(host: RemoteHost, remoteCase: RemoteCase): Sessi
     extraSshOptions: host.extraSshOptions,
   };
 }
+
+/**
+ * COD-105 — build a NON-owned `SessionRemote` for ATTACHING to a `codeman-*`
+ * session already running on a remote host (discovered via
+ * `listRemoteCodemanSessions`). The resulting session's pane runs
+ * `tmux -L codeman attach -t <remoteSessionName>` (see
+ * `buildRemoteAttachCommand`), and because we did NOT create the remote session,
+ * `owned: false` means closing the tab DETACHES rather than killing it.
+ *
+ * `remotePath` is informational here (the attached remote session keeps its own
+ * cwd); we record the host's nominal path so display helpers still show
+ * `user@host:path`.
+ */
+export function toAttachedSessionRemote(
+  host: RemoteHost,
+  remoteSessionName: string,
+  remotePath: string
+): SessionRemote {
+  return {
+    hostId: host.id,
+    label: host.label,
+    host: host.host,
+    username: host.username,
+    port: host.port,
+    remotePath,
+    commands: host.commands,
+    // Discovered + attached — another Codeman created it. Detach-not-kill.
+    owned: false,
+    remoteSessionName,
+    identityFile: host.identityFile,
+    socksProxy: host.socksProxy,
+    jumpHost: host.jumpHost,
+    extraSshOptions: host.extraSshOptions,
+  };
+}

src/tmux-manager.ts

@@ -812,6 +812,49 @@ export function buildRemoteKillCommand(options: { remote: SessionRemote; session
   return [ssh, ...connectionArgs, remoteSshTarget(remote), shellescape(killCmd)].join(' ');
 }
 
+/**
+ * COD-105 — build the SSH command that ATTACHES to an EXISTING `codeman-*` tmux
+ * session on the remote host (one this Codeman didn't create — discovered via
+ * `listRemoteCodemanSessions`). Sibling of `buildRemoteLaunchCommand`.
+ *
+ * Emits:
+ *   ssh -o BatchMode=yes -t [<COD-107 connection opts>] user@host \
+ *     'tmux -L codeman attach -t <session>'
+ *
+ * - `attach` (NOT `new-session -A`) so we only join an existing session; the
+ *   remote session keeps running independent of us, which is exactly why the
+ *   resulting Codeman session is NON-OWNED (see `SessionRemote.owned`): closing
+ *   the local tab must detach, never `kill-session` the remote.
+ * - The remote session name is shell-escaped so a value with metachars stays a
+ *   single token inside the quoted tmux invocation.
+ * - COD-107 — connection options (`-p`, `-i`, `-J`, SOCKS `-o ProxyCommand`,
+ *   arbitrary `-o`) come from the shared `buildSshConnectionArgs`, so attach
+ *   connects identically to launch / discovery / the prereq probe. `-t` sits
+ *   right after `ssh -o BatchMode=yes` (a PTY is required for interactive tmux).
+ */
+export function buildRemoteAttachCommand(remote: SessionRemote, remoteSessionName: string): string {
+  const tmuxInvocation = `tmux -L codeman attach -t ${shellescape(remoteSessionName)}`;
+  const [ssh, batchMode, ...connectionArgs] = buildSshConnectionArgs(remote);
+  const sshParts = [ssh, batchMode, '-t', ...connectionArgs, remoteSshTarget(remote), shellescape(tmuxInvocation)];
+  return sshParts.join(' ');
+}
+
+/**
+ * COD-105 — choose the right remote ssh command for a session's ownership:
+ *   - NON-owned (`remote.owned === false`): ATTACH to a discovered remote tmux
+ *     session by its EXISTING name (`remote.remoteSessionName`, falling back to
+ *     this session's deterministic name). We only join — never create.
+ *   - owned (default): LAUNCH/attach-or-create via `buildRemoteLaunchCommand`
+ *     (COD-104), which we then own and may explicitly kill.
+ */
+function buildRemoteSessionCommand(mode: SessionMode, remote: SessionRemote, sessionId: string): string {
+  if (remote.owned === false) {
+    const target = remote.remoteSessionName || remoteTmuxSessionName(sessionId);
+    return buildRemoteAttachCommand(remote, target);
+  }
+  return buildRemoteLaunchCommand({ mode, remote, sessionId });
+}
+
 /**
  * Set sensitive environment variables on a tmux session via setenv.
  * These are inherited by panes but not visible in ps output or tmux history.
@@ -1273,7 +1316,7 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
     try {
       // Build the full command to run inside tmux
       const localFullCmd = `${buildNofileLimitCommand()} && ${pathExport}${envExportsStr} && ${cmd}`;
-      const fullCmd = remote ? buildRemoteLaunchCommand({ mode, remote, sessionId }) : localFullCmd;
+      const fullCmd = remote ? buildRemoteSessionCommand(mode, remote, sessionId) : localFullCmd;
 
       // Create tmux session in three steps to handle cold-start (no server running)
       // and avoid the race where the command exits before remain-on-exit is set:
@@ -1521,7 +1564,7 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
     const config = niceConfig || DEFAULT_NICE_CONFIG;
     const cmd = wrapWithNice(baseCmd, config);
     const localFullCmd = `${buildNofileLimitCommand()} && ${pathExport}${envExportsStr} && ${cmd}`;
-    const fullCmd = remote ? buildRemoteLaunchCommand({ mode, remote, sessionId }) : localFullCmd;
+    const fullCmd = remote ? buildRemoteSessionCommand(mode, remote, sessionId) : localFullCmd;
 
     try {
       // For OpenCode: set sensitive env vars via tmux setenv before respawn
@@ -1650,6 +1693,39 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       return false;
     }
 
+    // COD-105 — DETACH-NOT-KILL for NON-owned remote sessions.
+    //
+    // When this session was created by ATTACHING a remote tmux session another
+    // Codeman owns (`remote.owned === false`), closing the tab must NOT propagate
+    // a remote `tmux kill-session` — that would nuke work the remote's own
+    // Codeman (or another instance) still relies on. We tear down ONLY the LOCAL
+    // pane that holds the ssh client: killing the local ssh sends SIGHUP to its
+    // remote `tmux attach`, which DETACHES (the durable remote session survives).
+    //
+    // This early return is the structural guarantee: no code below this point
+    // (now or in future for owned sessions) can ever issue a remote kill-session
+    // for a non-owned session. The only `kill-session` we run is on OUR LOCAL
+    // socket (`this.tmux()` = `tmux -L codeman` on THIS host), which kills the
+    // local pane — it does NOT reach the REMOTE socket.
+    if (session.remote && session.remote.owned === false) {
+      console.log(`[TmuxManager] DETACH (non-owned remote): tearing down local pane only for ${session.muxName}`);
+      if (isValidMuxName(session.muxName)) {
+        try {
+          // Local socket only — detaches the remote session by killing the local ssh pane.
+          execSync(`${this.tmux()} kill-session -t "${session.muxName}" 2>/dev/null`, {
+            timeout: EXEC_TIMEOUT_MS,
+          });
+        } catch {
+          // Local pane may already be gone.
+        }
+      }
+      this.lastPaneCount.delete(session.muxName);
+      this.sessions.delete(sessionId);
+      this.saveSessions();
+      this.emit('sessionKilled', { sessionId });
+      return true;
+    }
+
     // Get current PID (may have changed)
     const currentPid = this.getPanePid(session.muxName) || session.pid;
 

src/types/session.ts

@@ -96,6 +96,43 @@ export interface SessionRemote extends RemoteSshOptions {
   port?: number;
   remotePath: string;
   commands?: Partial<Record<RemoteCommandMode, string>>;
+  /**
+   * COD-105 — whether THIS Codeman created the remote tmux session.
+   *
+   * - `true` (default for COD-104 launched sessions): we own the remote session;
+   *   an explicit "kill" may propagate a remote `tmux kill-session`.
+   * - `false` (discovered + attached an existing remote session another Codeman
+   *   created): closing the local tab must DETACH only — we must NEVER issue a
+   *   remote `kill-session`, or we'd nuke work the remote's own Codeman (or
+   *   another instance) still relies on. See `killSession()` gate.
+   *
+   * Absent is treated as owned (legacy/COD-104 sessions persisted before this
+   * field existed were all launched by us).
+   */
+  owned?: boolean;
+  /**
+   * COD-105 — for a NON-owned (discovered + attached) session, the EXISTING
+   * remote tmux session name to `attach -t` (e.g. `codeman-disco1`). It differs
+   * from this Codeman's deterministic `codeman-<id>` name because the remote
+   * session was created elsewhere. Only meaningful when `owned === false`.
+   */
+  remoteSessionName?: string;
+}
+
+/**
+ * COD-105 — a `codeman-*` tmux session discovered on a remote host's
+ * `tmux -L codeman` socket (may have been created by the remote's own Codeman,
+ * another instance, or this one). Returned by `listRemoteCodemanSessions`.
+ */
+export interface RemoteSessionInfo {
+  /** tmux session name (always starts `codeman-`). */
+  name: string;
+  /** Whether a client is currently attached to the remote session. */
+  attached: boolean;
+  /** tmux `session_created` epoch seconds. */
+  created: number;
+  /** Number of windows in the remote session. */
+  windows: number;
 }
 
 /**

src/web/public/index.html

@@ -1915,6 +1915,17 @@
                 </div>
               </div>
             </details>
+            <!-- COD-105 — discover + attach existing remote tmux sessions this Codeman didn't create. -->
+            <details class="advanced-options" id="remoteDiscoverSection">
+              <summary>Discover existing sessions</summary>
+              <div class="advanced-options-content">
+                <span class="form-hint">Find <code>codeman-*</code> tmux sessions already running on this host (started by the remote's own Codeman or another instance) and attach to one. Attaching shares the session; closing the tab detaches it — it is never killed.</span>
+                <div class="form-row" style="margin-top: 8px;">
+                  <button type="button" class="btn-toolbar" id="remoteDiscoverBtn" onclick="app.discoverRemoteSessions()">Discover existing sessions</button>
+                </div>
+                <div id="remoteDiscoverResults" class="remote-discover-results"></div>
+              </div>
+            </details>
           </div>
           <!-- Manage Tab -->
           <div class="modal-tab-content hidden" id="case-manage">

src/web/public/session-ui.js

@@ -1767,6 +1767,150 @@ Object.assign(CodemanApp.prototype, {
     }
   },
 
+  // ═══════════════════════════════════════════════════════════════
+  // COD-105 — Discover + attach existing remote tmux sessions
+  // ═══════════════════════════════════════════════════════════════
+
+  /** Read the remote-host fields from the remote-case form into a host payload. */
+  _readRemoteHostFromForm() {
+    const hostId = document.getElementById('remoteHostId').value.trim();
+    const host = document.getElementById('remoteHostAddress').value.trim();
+    const username = document.getElementById('remoteHostUsername').value.trim();
+    const portRaw = document.getElementById('remoteHostPort').value.trim();
+    const identityFile = document.getElementById('remoteHostIdentityFile').value.trim();
+    const socksProxy = document.getElementById('remoteHostSocksProxy').value.trim();
+    const jumpHost = document.getElementById('remoteHostJumpHost').value.trim();
+    const codexCommand = document.getElementById('remoteHostCodexCommand').value.trim();
+    const extraSshOptions = document.getElementById('remoteHostExtraSshOptions').value
+      .split('\n')
+      .map(line => line.trim())
+      .filter(line => line.length > 0);
+    let port;
+    if (portRaw) {
+      const n = Number(portRaw);
+      if (Number.isInteger(n) && n >= 1 && n <= 65535) port = n;
+    }
+    return {
+      id: hostId,
+      label: hostId,
+      host,
+      username,
+      ...(port ? { port } : {}),
+      ...(identityFile ? { identityFile } : {}),
+      ...(socksProxy ? { socksProxy } : {}),
+      ...(jumpHost ? { jumpHost } : {}),
+      ...(extraSshOptions.length ? { extraSshOptions } : {}),
+      ...(codexCommand ? { commands: { codex: codexCommand } } : {}),
+    };
+  },
+
+  /**
+   * Explicit Discover action (Decision A — never auto-runs on host select).
+   * Saves the host config (idempotent), then queries the host for `codeman-*`
+   * tmux sessions it didn't create and renders an Attach action per session.
+   */
+  async discoverRemoteSessions() {
+    const results = document.getElementById('remoteDiscoverResults');
+    const btn = document.getElementById('remoteDiscoverBtn');
+    const hostPayload = this._readRemoteHostFromForm();
+    if (!hostPayload.id || !hostPayload.host || !hostPayload.username) {
+      this.showToast('Fill in Host ID, address, and username first', 'error');
+      return;
+    }
+    if (!/^[a-zA-Z0-9_-]+$/.test(hostPayload.id)) {
+      this.showToast('Invalid Host ID. Use letters, numbers, hyphens, underscores.', 'error');
+      return;
+    }
+    if (btn) btn.disabled = true;
+    if (results) results.innerHTML = '<div class="form-hint">Discovering…</div>';
+    try {
+      // Persist the host so the discovery endpoint can resolve it by id (idempotent).
+      const hostRes = await fetch('/api/remote-hosts', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify(hostPayload)
+      });
+      const hostData = await hostRes.json();
+      if (!hostData.success && hostData.errorCode !== 'ALREADY_EXISTS') {
+        throw new Error(hostData.error || 'Failed to save remote host');
+      }
+      const res = await fetch(`/api/remote-hosts/${encodeURIComponent(hostPayload.id)}/sessions`);
+      const data = await res.json();
+      if (!data.success) throw new Error(data.error || 'Discovery failed');
+      this._renderDiscoveredSessions(hostPayload.id, data.data.sessions || []);
+    } catch (err) {
+      console.error('Discover remote sessions failed:', err);
+      if (results) results.innerHTML = `<div class="form-hint" style="color: var(--error, #e06c75);">${escapeHtml(err.message)}</div>`;
+    } finally {
+      if (btn) btn.disabled = false;
+    }
+  },
+
+  /** Render the discovered remote sessions with an Attach action each. */
+  _renderDiscoveredSessions(hostId, sessions) {
+    const results = document.getElementById('remoteDiscoverResults');
+    if (!results) return;
+    if (!sessions.length) {
+      results.innerHTML = '<div class="form-hint">No <code>codeman-*</code> sessions running on this host (or it is unreachable).</div>';
+      return;
+    }
+    const now = Math.floor(Date.now() / 1000);
+    const rows = sessions.map(s => {
+      const ageSecs = Math.max(0, now - (s.created || 0));
+      const age = ageSecs < 3600 ? `${Math.floor(ageSecs / 60)}m` : ageSecs < 86400 ? `${Math.floor(ageSecs / 3600)}h` : `${Math.floor(ageSecs / 86400)}d`;
+      const attachedBadge = s.attached
+        ? '<span class="case-location-badge" style="background: var(--accent, #61afef);">attached</span>'
+        : '';
+      return `
+        <div class="remote-discover-item">
+          <div class="remote-discover-info">
+            <span class="remote-discover-name">${escapeHtml(s.name)} ${attachedBadge}</span>
+            <span class="form-hint">age ${age} · ${s.windows || 1} window(s)</span>
+          </div>
+          <button type="button" class="btn-toolbar" onclick="app.attachDiscoveredSession('${escapeHtml(hostId)}', '${escapeHtml(s.name)}')">Attach</button>
+        </div>`;
+    }).join('');
+    results.innerHTML = rows;
+  },
+
+  /**
+   * Create a NON-owned session that attaches to a discovered remote tmux session.
+   * Closing this tab detaches — it never kills the remote session.
+   */
+  async attachDiscoveredSession(hostId, remoteSessionName) {
+    try {
+      const createRes = await fetch('/api/sessions', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          mode: 'shell',
+          name: remoteSessionName,
+          attachRemoteSession: { hostId, remoteSessionName },
+        })
+      });
+      const createData = await createRes.json();
+      if (!createData.success) throw new Error(createData.error || 'Failed to create session');
+      const id = createData.data.session.id;
+      await fetch(`/api/sessions/${id}/shell`, { method: 'POST' });
+      const dims = this.getTerminalDimensions();
+      if (dims) {
+        await fetch(`/api/sessions/${id}/resize`, {
+          method: 'POST',
+          headers: { 'Content-Type': 'application/json' },
+          body: JSON.stringify(dims)
+        });
+      }
+      this.closeCreateCaseModal();
+      this.showToast(`Attached to ${remoteSessionName} (detach on close)`, 'success');
+      this.activeSessionId = id;
+      await this.selectSession(id);
+      if (this.terminal && typeof this.terminal.focus === 'function') this.terminal.focus();
+    } catch (err) {
+      console.error('Attach discovered session failed:', err);
+      this.showToast('Failed to attach: ' + err.message, 'error');
+    }
+  },
+
   // ═══════════════════════════════════════════════════════════════
   // Case Management (reorder + delete)
   // ═══════════════════════════════════════════════════════════════

src/web/public/styles.css

@@ -3933,6 +3933,37 @@ body.touch-device .terminal-container .xterm .xterm-helper-textarea {
   transition: background var(--transition-smooth);
 }
 
+/* COD-105 — discovered remote tmux sessions list (remote-case flow). */
+.remote-discover-results {
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+  margin-top: 8px;
+}
+
+.remote-discover-item {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+  padding: 8px 10px;
+  background: rgba(255, 255, 255, 0.03);
+  border: 1px solid rgba(255, 255, 255, 0.06);
+  border-radius: 6px;
+}
+
+.remote-discover-info {
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+  min-width: 0;
+}
+
+.remote-discover-name {
+  font-weight: 600;
+  font-size: 0.85rem;
+}
+
 .case-manage-item:hover {
   background: rgba(255, 255, 255, 0.06);
 }

src/web/routes/case-routes.ts

@@ -9,7 +9,7 @@ import { existsSync, mkdirSync, writeFileSync, readdirSync } from 'node:fs';
 import fs from 'node:fs/promises';
 import { join, resolve } from 'node:path';
 import { homedir } from 'node:os';
-import type { ApiResponse, CaseInfo } from '../../types.js';
+import type { ApiResponse, CaseInfo, RemoteSessionInfo } from '../../types.js';
 import { ApiErrorCode, createErrorResponse, getErrorMessage } from '../../types.js';
 import {
   CreateCaseSchema,
@@ -26,6 +26,7 @@ import type { EventPort, ConfigPort } from '../ports/index.js';
 import { dataPath, getDataDir } from '../../config/instance.js';
 import {
   checkRemoteTmuxAvailable,
+  listRemoteCodemanSessions,
   readRemoteCases,
   readRemoteHosts,
   remoteDisplayPath,
@@ -167,6 +168,23 @@ export function registerCaseRoutes(app: FastifyInstance, ctx: EventPort & Config
 
   app.get('/api/remote-hosts', async () => readRemoteHosts(CODEMAN_CONFIG_DIR));
 
+  // COD-105 — discover `codeman-*` tmux sessions already running on a remote
+  // host (created by the remote's own Codeman, another instance, or this one)
+  // so the operator can attach to one this Codeman didn't launch. Explicit
+  // trigger only (Decision A): the frontend calls this on a "Discover" click,
+  // never automatically on host select. listRemoteCodemanSessions never throws
+  // (returns [] on unreachable/no-tmux/no-sessions) and is ssh-guarded under test.
+  app.get(
+    '/api/remote-hosts/:hostId/sessions',
+    async (req): Promise<ApiResponse<{ sessions: RemoteSessionInfo[] }>> => {
+      const { hostId } = req.params as { hostId: string };
+      const host = (await readRemoteHosts(CODEMAN_CONFIG_DIR)).find((item) => item.id === hostId);
+      if (!host) return createErrorResponse(ApiErrorCode.NOT_FOUND, 'Remote host not found');
+      const sessions = await listRemoteCodemanSessions(host);
+      return { success: true, data: { sessions } };
+    }
+  );
+
   app.post('/api/remote-hosts', async (req): Promise<ApiResponse<{ host: unknown }>> => {
     const host = parseBody(RemoteHostSchema, req.body);
     const hosts = await readRemoteHosts(CODEMAN_CONFIG_DIR);

src/web/routes/session-routes.ts

@@ -73,7 +73,13 @@ import { RunSummaryTracker } from '../../run-summary.js';
 import { MAX_INPUT_LENGTH, MAX_SESSION_NAME_LENGTH } from '../../config/terminal-limits.js';
 import { MAX_PASTE_IMAGE_BYTES } from '../../config/buffer-limits.js';
 import { dataPath, getDataDir } from '../../config/instance.js';
-import { checkRemoteTmuxAvailable, readRemoteCases, readRemoteHosts, toSessionRemote } from '../../remote-hosts.js';
+import {
+  checkRemoteTmuxAvailable,
+  readRemoteCases,
+  readRemoteHosts,
+  toAttachedSessionRemote,
+  toSessionRemote,
+} from '../../remote-hosts.js';
 import { LRUMap } from '../../utils/lru-map.js';
 
 // Path to linked-cases registry (same file used by case-routes resolveCasePath)
@@ -292,7 +298,21 @@ export function registerSessionRoutes(
     }
 
     const body = parseBody(CreateSessionSchema, req.body);
-    const workingDir = body.workingDir || process.cwd();
+    let workingDir = body.workingDir || process.cwd();
+    let remote = undefined;
+
+    // COD-105 — attach to a discovered (non-owned) remote tmux session. The
+    // remote session is already running, so we skip the tmux-prereq probe and
+    // build a NON-owned SessionRemote (detach-not-kill on close). Remote CASE
+    // creation (owned durable sessions) is handled by the dedicated case-create
+    // endpoint below, which #145 consolidated remote-host resolution into.
+    if (body.attachRemoteSession) {
+      const { hostId, remoteSessionName } = body.attachRemoteSession;
+      const host = (await readRemoteHosts(CODEMAN_CONFIG_DIR)).find((item) => item.id === hostId);
+      if (!host) return createErrorResponse(ApiErrorCode.NOT_FOUND, 'Remote host not found');
+      workingDir = `${host.username}@${host.host}:${remoteSessionName}`;
+      remote = toAttachedSessionRemote(host, remoteSessionName, workingDir);
+    }
 
     // Validate workingDir exists and is a directory
     if (body.workingDir) {
@@ -447,6 +467,7 @@ export function registerSessionRoutes(
       envOverrides: body.envOverrides,
       effort: body.effort,
       tmuxHistoryLimit: terminalHistoryConfig.tmuxHistoryLimit,
+      remote,
     });
 
     ctx.addSession(session);

src/web/schemas.ts

@@ -192,6 +192,22 @@ export const CreateSessionSchema = z.object({
     .max(100)
     .regex(/^[a-f0-9-]+$/, 'resumeSessionId must be a valid UUID')
     .optional(),
+  /**
+   * COD-105 — attach to an EXISTING remote tmux session discovered via
+   * `GET /api/remote-hosts/:hostId/sessions` (one this Codeman didn't create).
+   * The resulting session is NON-owned (closing it detaches, never kills the
+   * remote). `remoteSessionName` is a discovered `codeman-*` tmux session name.
+   */
+  attachRemoteSession: z
+    .object({
+      hostId: z.string().min(1).max(200),
+      remoteSessionName: z
+        .string()
+        .min(1)
+        .max(200)
+        .regex(/^codeman-[a-zA-Z0-9._-]+$/, 'remoteSessionName must be a codeman-* tmux session name'),
+    })
+    .optional(),
 });
 
 /**