Expose Hunk selections to coding agents, with exact text selection when possible

[benvinegar]

Problem

Hunk should make it easy to hand the currently relevant diff context to a coding agent.

The user request here is broader than "export the focused hunk": ideally, if the user selects text in Hunk, that selection should become available to their coding agent. At minimum, Hunk should have a first-class way to publish the current hunk/selection to an external agent workflow.

Related work already in flight

There are already open PRs that appear to cover important pieces of this:

• feat: export selected hunk to pi #73 — feat: export selected hunk to pi
• feat: add Hunk notify stream #77 — feat: add Hunk notify stream

From those PR descriptions:

• feat: export selected hunk to pi #73 adds a p shortcut and writes .hunk/pi-selection.json
• feat: add Hunk notify stream #77 adds a notify stream and hunk session selection ...

That looks like good foundation work, but there is not yet a clear issue tracking the end-user capability we want to ship.

Goal

Let Hunk publish the user's current review context to a coding agent in a structured, low-friction way.

Potential levels of support:

1. focused hunk export
2. published selection export (p-style explicit action)
3. exact text selection export when terminal selection support makes that possible

Scope / design questions

• Should Hunk bless the file bridge (.hunk/pi-selection.json), the session CLI + notify stream, or both?
• Should the integration be Pi-specific or generic enough for any local coding agent?
• Is the primary UX:
  • explicit publish (p)
  • always-current focused selection
  • both?
• If arbitrary text selection is not practical cross-terminal, is the focused hunk the right stable primitive to ship first?

Acceptance criteria

• A user can publish the current review context from Hunk to a coding agent workflow without copy/paste.
• The exported payload includes enough structure to be useful:
  • repo root (when available)
  • file path / previous path
  • hunk or selection range
  • diff snippet / patch
  • human-readable prompt text
• The transport is documented and stable enough for external tooling to rely on.
• If exact text selection is not supported initially, document that the first shipped unit is the focused/published hunk.

Notes

This issue is intentionally outcome-focused so the work can reuse or supersede #73 / #77 as needed without losing sight of the user-facing goal.