feat(deepseek): add DeepSeek Harness (dsh) as a ninth CLI run mode

Adds `mode: 'deepseek'` alongside claude/shell/opencode/codex/gemini/
antigravity/pi/grok, plus a shortcut that opens the harness's own browser UI
as a Codeman web tab.

DeepSeek is wired unlike its siblings in three ways, each of which is the
reason for a design decision rather than an accident:

1. The agent is a PROFILE, not the binary. `dsh` is a launcher over
   $DSH_HOME/profiles/<name>, and DeepSeek ships only `web`, `headless` and
   `base` -- the interactive terminal front door is always a third-party
   plugin. So availability is two questions: `isDeepSeekAvailable()` (binary)
   and `isDeepSeekRunnable()` (binary AND a pane-capable profile). The Run
   button gates on the latter, because reporting only the binary would spawn a
   pane that dies on arrival. When the binary is present but no profile is,
   the run menu offers to install one (POST /api/deepseek/install-profile).

2. The permission switch is an env var, not a flag. The harness has no
   command-line permission option; its sandbox/approval rows read
   DSH_PERMISSION_MODE (read-only / workspace-write / danger-full-access).
   Exported via `tmux setenv`, never on the spawn line. Absent = the harness's
   own workspace-write, which still asks, so the multi-user clamp is the
   only-if-sent branch and clamps to workspace-write, never read-only.

3. It is the only non-claude mode that passes hooksAvailableForMode(), and it
   earned that. The terminal front door reports idle/working/blocked to a
   supervising process over a generic env-gated contract; a generated shim
   (deepseek-status-shim.ts) makes Codeman that supervisor and forwards each
   report to /api/hook-event as stop / agent_working / permission_prompt. So a
   dsh session gets definitive respawn triggers, real wait-endpoint signals and
   real Approvals Inbox items instead of output-stabilization guesswork.
   `agent_working` is new (157th SSE constant) and joins
   APPROVAL_RESOLVING_EVENTS so a dialog answered in the terminal clears its
   alert at once.

The resolver needs the strictest identity probe of the family: `dsh` is not
merely a squattable npm name, Debian ships an unrelated `dsh` (dancer's shell),
so `dsh --help` must print the harness's own banner before a candidate is
handed a spawn line.

Model is deliberately not a session field -- it is a composition entry in the
profile's config tree. Env allowlist gains DSH_* and DEEPSEEK_* only; provider
keys named by a settings-file `apiKeyEnv` stay out, which is pi's
34-provider-key problem in a new shape.

Verified live against dsh 0.1.1-rc.2 and @deepseek-harness-tui/dsh-tui: the
status endpoint's two-part answer, the no-profile refusal, the profile
bootstrap, a real session whose pane runs `dsh --profile dsh-tui` with the
permission mode injected via setenv, and the full status bridge -- a
send-and-wait returned signal "stop" from a real turn, and blocked/working
created and cleared an Approvals Inbox item.

Docs: docs/deepseek-integration.md (guide), docs/deepseek-integration-plan.md
(decisions + honest gaps). Tests: test/deepseek-mode.test.ts,
test/deepseek-cli-resolver.test.ts.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/session.ts

@@ -52,6 +52,7 @@ import {
   type AntigravityConfig,
   type PiConfig,
   type GrokConfig,
+  type DeepSeekConfig,
   type SessionRemote,
   type SessionDocker,
 } from './types.js';
@@ -178,7 +179,8 @@ export function isExternalCliMode(mode: SessionMode): boolean {
     mode === 'gemini' ||
     mode === 'antigravity' ||
     mode === 'pi' ||
-    mode === 'grok'
+    mode === 'grok' ||
+    mode === 'deepseek'
   );
 }
 
@@ -196,6 +198,8 @@ function getModeLabel(mode: SessionMode): string {
       return 'Pi';
     case 'grok':
       return 'Grok';
+    case 'deepseek':
+      return 'DeepSeek';
     case 'shell':
       return 'Shell';
     case 'claude':
@@ -521,6 +525,9 @@ export class Session extends EventEmitter {
   private _piConfig: PiConfig | undefined;
   // Grok configuration (only for mode === 'grok')
   private _grokConfig: GrokConfig | undefined;
+
+  // DeepSeek Harness configuration (only for mode === 'deepseek')
+  private _deepSeekConfig: DeepSeekConfig | undefined;
   private _resumeSessionId: string | undefined;
 
   // Ephemeral env overrides (e.g., CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS). Exported by tmux
@@ -618,6 +625,8 @@ export class Session extends EventEmitter {
       piConfig?: PiConfig;
       /** Grok configuration (only for mode === 'grok') */
       grokConfig?: GrokConfig;
+      /** DeepSeek Harness configuration (only for mode === 'deepseek') */
+      deepSeekConfig?: DeepSeekConfig;
       /** Resume a previous Claude conversation (used after server reboot) */
       resumeSessionId?: string;
       /** Extra env vars exported to the CLI at spawn time (no disk persistence) */
@@ -727,6 +736,11 @@ export class Session extends EventEmitter {
       this._piConfig = config.piConfig;
     }
 
+    // Apply DeepSeek Harness configuration
+    if (config.deepSeekConfig) {
+      this._deepSeekConfig = config.deepSeekConfig;
+    }
+
     // Apply Grok configuration
     if (config.grokConfig) {
       this._grokConfig = config.grokConfig;
@@ -1325,6 +1339,7 @@ export class Session extends EventEmitter {
       antigravityConfig: this._antigravityConfig,
       piConfig: this._piConfig,
       grokConfig: this._grokConfig,
+      deepSeekConfig: this._deepSeekConfig,
       resumeSessionId: this._resumeSessionId,
       effort: this._effort,
       // COD-118: runtime-only — surfaced so the frontend can require explicit user
@@ -1501,7 +1516,8 @@ export class Session extends EventEmitter {
               this.mode === 'gemini' ||
               this.mode === 'antigravity' ||
               this.mode === 'pi' ||
-              this.mode === 'grok'
+              this.mode === 'grok' ||
+              this.mode === 'deepseek'
           ),
         })
       );
@@ -1572,6 +1588,7 @@ export class Session extends EventEmitter {
       antigravityConfig: this._antigravityConfig,
       piConfig: this._piConfig,
       grokConfig: this._grokConfig,
+      deepSeekConfig: this._deepSeekConfig,
       resumeSessionId: this._resumeSessionId,
       envOverrides: this._envOverrides,
       effort: this._effort,
@@ -1831,6 +1848,7 @@ export class Session extends EventEmitter {
             antigravityConfig: this._antigravityConfig,
             piConfig: this._piConfig,
             grokConfig: this._grokConfig,
+            deepSeekConfig: this._deepSeekConfig,
             resumeSessionId: this._resumeSessionId,
             envOverrides: this._envOverrides,
             effort: this._effort,
@@ -1924,6 +1942,12 @@ export class Session extends EventEmitter {
       if (this.mode === 'grok') {
         throw new Error('Grok sessions require tmux. Direct PTY fallback is not supported.');
       }
+      // DeepSeek sessions require tmux for DEEPSEEK_API_KEY / DSH_PERMISSION_MODE
+      // injection via setenv — and for the HERDR_* status-bridge triple, without
+      // which the mode silently loses its definitive idle/blocked signals.
+      if (this.mode === 'deepseek') {
+        throw new Error('DeepSeek Harness sessions require tmux. Direct PTY fallback is not supported.');
+      }
       try {
         // Pass --session-id to use the SAME ID as the Codeman session
         // This ensures subagents can be directly matched to the correct tab