fix: separate Navigator from subagent delegation

[dbpolito]

Ticket

SKIPPED

Description

Reserve Navigator for explicitly requested native-session workflows while directing ordinary delegation to OpenCode's built-in task tool. Created sessions now inherit the caller's agent, model, and variant, and V2 operations reject unknown agent names before prompt admission.

Checklist

Delegation Boundaries

• Restrict Navigator guidance to explicit native-session and worktree workflows
• Direct subagent delegation and waiting to the built-in task tool

Session Context

• Inherit caller agent, model, and variant when creating sessions
• Validate V2 agent names before creating or steering sessions

Documentation

• Update adapter and web documentation with the revised lifecycle behavior
• Replace delegation-oriented Navigator alias examples

Validation

• Verify that bun run compile completes successfully
• Confirm that bun run typecheck reports no diagnostics
• Check that all core and OpenCode adapter tests pass

[kompassdev]

★★★★☆

Navigator cleanly separates native-session orchestration from subagent delegation, and the caller-inheritance + V2 agent validation logic is well covered by the new tests. Two medium concerns:

• (inline) assertKnownV2Agent runs after worktree creation on the new_worktree path, so an unknown agent now leaks a worktree with no error context.
• packages/opencode/navigator.ts:898 — V2 session_create and session_send now hard-depend on client.v2.agent.list for every call that selects an agent (including caller-inherited agents), but getNavigatorCompatibilityWarning only verifies client.v2.session methods for the V2 path. If a runtime-"compatible" OpenCode version lacks v2.agent.list, every agent-carrying V2 create/send throws an unrelated "OpenCode agent list" failure instead of operating or emitting the Navigator-incompatibility warning. Worth confirming 1.17.12 ships agent.list, or adding it to the V2 hasMethods list (and degrading gracefully when missing).

[dbpolito]

Addressed the client.v2.agent.list compatibility concern from review 4798096892 in 6965a77. The V2 compatibility probe now requires agent.list, so runtimes missing that API emit the existing Navigator incompatibility warning instead of failing later during create/send. Added regression coverage for the missing-method case.