feat(cli): extend run command with port, attach, session-id, on-complete, and json options

Implement all 5 CLI extension options for external orchestration:

- --port <port>: Start server on port, or attach if port occupied
- --attach <url>: Connect to existing opencode server
- --session-id <id>: Resume existing session instead of creating new
- --on-complete <command>: Execute shell command with env vars on completion
- --json: Output structured RunResult JSON to stdout

Refactor runner.ts into focused modules:
- agent-resolver.ts: Agent resolution logic
- server-connection.ts: Server connection management
- session-resolver.ts: Session create/resume with retry
- json-output.ts: Stdout redirect + JSON emission
- on-complete-hook.ts: Shell command execution with env vars

Fixes #1586

src/cli/run/agent-resolver.ts

@@ -0,0 +1,69 @@
+import pc from "picocolors"
+import type { RunOptions } from "./types"
+import type { OhMyOpenCodeConfig } from "../../config"
+
+const CORE_AGENT_ORDER = ["sisyphus", "hephaestus", "prometheus", "atlas"] as const
+const DEFAULT_AGENT = "sisyphus"
+
+type EnvVars = Record<string, string | undefined>
+
+const normalizeAgentName = (agent?: string): string | undefined => {
+  if (!agent) return undefined
+  const trimmed = agent.trim()
+  if (!trimmed) return undefined
+  const lowered = trimmed.toLowerCase()
+  const coreMatch = CORE_AGENT_ORDER.find((name) => name.toLowerCase() === lowered)
+  return coreMatch ?? trimmed
+}
+
+const isAgentDisabled = (agent: string, config: OhMyOpenCodeConfig): boolean => {
+  const lowered = agent.toLowerCase()
+  if (lowered === "sisyphus" && config.sisyphus_agent?.disabled === true) {
+    return true
+  }
+  return (config.disabled_agents ?? []).some(
+    (disabled) => disabled.toLowerCase() === lowered
+  )
+}
+
+const pickFallbackAgent = (config: OhMyOpenCodeConfig): string => {
+  for (const agent of CORE_AGENT_ORDER) {
+    if (!isAgentDisabled(agent, config)) {
+      return agent
+    }
+  }
+  return DEFAULT_AGENT
+}
+
+export const resolveRunAgent = (
+  options: RunOptions,
+  pluginConfig: OhMyOpenCodeConfig,
+  env: EnvVars = process.env
+): string => {
+  const cliAgent = normalizeAgentName(options.agent)
+  const envAgent = normalizeAgentName(env.OPENCODE_DEFAULT_AGENT)
+  const configAgent = normalizeAgentName(pluginConfig.default_run_agent)
+  const resolved = cliAgent ?? envAgent ?? configAgent ?? DEFAULT_AGENT
+  const normalized = normalizeAgentName(resolved) ?? DEFAULT_AGENT
+
+  if (isAgentDisabled(normalized, pluginConfig)) {
+    const fallback = pickFallbackAgent(pluginConfig)
+    const fallbackDisabled = isAgentDisabled(fallback, pluginConfig)
+    if (fallbackDisabled) {
+      console.log(
+        pc.yellow(
+          `Requested agent "${normalized}" is disabled and no enabled core agent was found. Proceeding with "${fallback}".`
+        )
+      )
+      return fallback
+    }
+    console.log(
+      pc.yellow(
+        `Requested agent "${normalized}" is disabled. Falling back to "${fallback}".`
+      )
+    )
+    return fallback
+  }
+
+  return normalized
+}