feat(config): add a flock { } configuration section

[abeljim8am]

Stacked on #27 (feat/default-setup-phase-0). Review that one first; this PR's diff is only the Phase 1 commit.

Why

Phase 0 made the two Flock plugins configurable in one place by registering them as plugin aliases — but that place is a plugins { } alias body, which is plumbing, not a settings surface. It also means folder args are written twice (once per alias) and expressed in the plugins' wire format: root_dirs "~/src;~/work" rather than a list, devcontainers_enabled "true" rather than a bool.

Phase 1 gives Flock a real configuration section:

flock {
    root_dirs "~/src" "~/work"
    individual_dirs "~/dotfiles"
    devcontainers true
    ssh true
}

Values are merged underneath the flock-selector and flock-sidebar aliases, so the selector, the Super s keybinding and the sidebar in every session all derive from one source — while anything stated on a plugin or in a layout still wins, so a single layout can opt out.

Ergonomics

• Lists take multiple entries (root_dirs "~/src" "~/work") and the ;-joined form, so a value copied out of a layout still works.
• Flags take the KDL bool (ssh true) and the quoted string (ssh "true") for the same reason.
• Unset means "say nothing", leaving the plugin's own default in force rather than overriding it with a zero value.
• An unrecognized key is a parse error, not a silent skip. A typo like root_dirs_typo would otherwise leave the selector mysteriously empty with nothing to point at.

Two design points worth your attention

1. The projection is computed on demand, not stored. Config::plugin_aliases_with_flock_defaults() builds it where the server consumes the aliases; Config.plugins stays pristine.

This is the important one. The stored aliases are what gets serialized back to disk — the configuration plugin writes the whole config, and the first-run wizard triggers it (I hit exactly this in #27, where the wizard wrote a config.kdl into a test fixture). Folding the projection into Config.plugins would be a one-way door: the next write copies the values into each alias body, where they outrank flock { } itself, so editing the block would silently stop having any effect. Tests pin both halves — the stored alias stays clean, and a to_string round-trip must not leak root_dirs into the plugins block.

2. FlockConfig needs to_kdl, not just from_kdl — or that same write-back silently drops the section. Covered by a round-trip test.

Deviation from the plan

The plan called for injecting at plugin-load time in zellij-server, so a layout naming zellij:flock-selector directly would also pick the section up. I projected onto the aliases instead: one seam in zellij-utils that is fully unit-testable, versus threading config into the plugin thread and keeping several matching call sites consistent — where a missed seam fails silently, which is the failure mode that already bit this area twice.

The accepted cost is that a layout referencing zellij:flock-* directly gets no flock { } values and keeps whatever args it states. That is narrow now that the bundled layouts and the README all use the alias form, and it is documented in the README, the CHANGELOG, and the method's doc comment.

Deferred to Phase 2

The key to disable selector-on-startup. That behavior does not exist yet, and shipping a config key that does nothing is worse than adding it when it works.

Verification

• cargo xtask test — 2353 passing, 0 failures. cargo xtask format --check clean.
• 14 new tests: multi-entry and ;-joined lists, bool and string flags, unknown-key error, arg-name translation, both plugins receiving identical config, alias-body-wins precedence, empty-section no-op, projection-not-stored, write-back round-trip plus the no-leak assertion, merge precedence in both directions, and that the shipped default ships the section commented out with both aliases present.
• Snapshot changes are purely additive (zero removed lines) — just the new empty flock field in the config debug output.
• Checked against the built binary: with only a flock { } block in config.kdl, action dump-layout shows root_dirs "~/src;~/work", individual_dirs "~/dotfiles" and devcontainers_enabled "true" resolved onto the sidebar inside the bundled layout, which never mentions them. Ran with a pre-seeded config.kdl so the first-run wizard could not interfere — the lesson from feat(setup): make a fresh install land in Flock, not plain Zellij #27.
• Both README snippets were run through setup --check ([CONFIG FILE]: Well defined.) rather than shipped untested.

🤖 Generated with Claude Code

[abeljim]

Superseded by mega PR #35