feat(jj): support multi-file merge via DiffviewOpen

[dlyongemallo]

Proposed alternative to using DiffviewMergeFiles directly as a jj merge tool.

Relates to #267.

[Copilot]

Pull request overview

This PR implements the feature requested in issue #267: using jj (Jujutsu) as an interactive merge tool inside diffview. Because jj has no staging index, the existing s/- (toggle_stage_entry) staging action is repurposed on jj conflict views to "save the current MERGED buffer and advance to the next conflict," with auto_close_on_empty closing the view after the final resolution. To support this, a new adapter capability has_staging() is introduced and used to branch action-applicability and auto-close policy between staging adapters (git/hg/p4) and index-less ones (jj). The jj merge-context query is also hardened to locate the nearest ancestor merge, so propagated conflicts (where @ is a linear descendant of a conflicted merge) resolve correctly.

Changes:

• Add VCSAdapter:has_staging() (base: true; jj: false) and gate toggle_stage_entry via a new stage_or_resolve action tag plus a content-based resolve path in the diff listeners.
• Rework jj _query_merge_context to anchor on the nearest ancestor merge (latest(ancestors(@) & merges(), 1)) and base at fork_point(<merge>-), and wrap parse_revs @- in latest(...) for merge-safe parent resolution.
• Update the auto-close policy to gate index-less adapters on a had_conflicts latch, plus docs, keymap descriptions, and unit/functional tests.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lua/diffview/vcs/adapters/jj/init.lua	Merge-safe parse_revs, nearest-ancestor-merge context query, and has_staging() override returning false.
lua/diffview/vcs/adapter.lua	New base has_staging() capability method defaulting to true.
lua/diffview/actions.lua	New stage_or_resolve action tag and applicability logic branching on has_staging().
lua/diffview/scene/views/diff/listeners.lua	Content-based conflict resolve/advance path and had_conflicts-gated auto-close.
lua/diffview/scene/views/standard/standard_view.lua	set_file_in_flight() accessor so auto-close can defer teardown.
lua/diffview/config.lua, doc/diffview.txt, doc/diffview_defaults.txt	Keymap-description and help updates for the jj save-and-advance behavior.
lua/diffview/tests/functional/*	New jj_save_and_advance_spec.lua and updates to actions/adapter/diff_view specs.

A note for the author (outside the diff, so not filed as an inline comment): doc/diffview_changelog.txt:35-37 still states that staging actions including s are "no-ops in jj." That claim is now inaccurate for conflict views, and the changelog's own policy is to list notable feature additions — consider updating it.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.