feat(chat): support native Grok conversations #776

Problem

Grok panes can use Terminal, but Chat has no native Grok transcript reader and shows “Conversation unavailable — show terminal output”. This is a feature request for native Chat support, not a demonstrated regression: terminal fallback is the documented behavior for unsupported agents.

Source review found no Grok reader in the conversation resolver, including when Herdr supplies an explicit agent session ID. Separately, isolated Grok 1.0.50 / Herdr 0.9.3 tests found that an in-TUI /resume does not fire SessionStart, leaving Herdr's session ID stale. A reader therefore needs both native history parsing and a trustworthy current-session binding.

Proposal

Read the active session's native updates.jsonl through the existing conversation API, pager and Chat UI. Render user/assistant text and expandable tool activity, apply logical rewind markers before paging, and invalidate stale cursors and expanded-output references. Reading history should not invoke a model. Keep Terminal available for approvals and unavailable histories.

Use an opt-in status-line helper to obtain Grok's current session ID and transcript path after an idle resume, refresh Herdr, and record short-lived evidence tied to the pane and process. Preserve an existing status-line command and make no automatic configuration changes. Herdr 0.9.3 currently needs the compatibility value session_start_source: "new" to replace an ID even for resume; a documented switch/refresh operation would be preferable.

A proposed implementation includes Linux, macOS and Windows paths, reusing existing process discovery. Native macOS/Windows behavior remains untested; platform reports can be addressed in the accompanying PR. Reasoning, images, child-session expansion and approval handling are outside this first scope.

Where

Chat and prompt cards

Workarounds and alternatives

Use Terminal today. Relying solely on Herdr's session ID can select stale history after resume; guessing by newest file or cwd is unsuitable. A future Herdr/Grok integration that reports every session switch could replace the opt-in helper.