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What and why

atc's workspace provider must talk to meta only through meta … --json (no reading meta's files, env vars or layout). To decide whether a directory belongs to a meta workspace at all, it needs meta to say so. Today meta project list --recursive --json outside a workspace exits 1 with only a stderr message, the same as any real failure, so atc had to look for meta's config file names on disk itself.

With --json (before or after the command), meta's "Could not find meta config file" branch in meta_cli/src/main.rs now also prints one JSON object on stdout:

{"error":{"code":"config_not_found","message":"Could not find meta config file '.meta.yaml'\nSearched from /some/dir up to root"}}

• Exit status stays 1: the command did not run.
• Stderr text is unchanged.
• Without --json, the output is unchanged (stdout stays empty). The one behaviour change, with or without --json, is in a .worktrees/<name> directory with no config; see below.
• code is the contract; the message is for people. Rebased on refactor!: meta_cli reads only .meta.yaml #47 (tasks/harmony-2878, .meta.yaml only).
• The code is config_not_found rather than "not a workspace": an explicit --config that doesn't exist reaches the same error inside a workspace, and, for plugin commands, inside a worktree set (see below). Callers that pass no --config (atc) can read it as "no meta workspace here".

Every command that needs a config goes through this branch (plugin commands and meta exec); context, init, plugin management, help and git clone don't.

Inside a .worktrees/<name> directory with no config (for example a plain git worktree add .worktrees/x), meta took a "degraded" path that ran any command as a raw program in the set's checkouts, so meta project list --json tried to run a project binary and printed loop results. Now a command that a plugin claims gets the same config-not-found error there (as JSON with --json), the same as outside a workspace: plugin commands need a config. meta exec keeps running in the set's checkouts. Which commands count as plugin commands depends on the installed plugins: without meta-project installed, meta project list there still runs a project program from PATH, as before. The error code is built in one helper, config_not_found, used by both places.

Tests

json_callers_without_a_config_get_a_json_error (tests/json_errors.rs, not unix-gated, so Windows CI runs it too):

• project list --recursive --json and --json git worktree list outside a workspace exit with status 1, print the JSON error with code = "config_not_found", and repeat the message on stderr;
• an explicit --config that doesn't exist, inside a workspace, gives the same error;
• a malformed .meta.yaml fails without claiming config_not_found;
• meta --json exec -- true outside a workspace gives the same error.

a_plugin_command_in_a_plain_git_worktree_needs_a_config (tests/plugin_routing.rs): in a plain Git worktree under .worktrees/x with no config, meta --json touch (claimed by a fake plugin) exits 1 with config_not_found and runs nothing; meta exec -- touch ran still runs there. It fails without the change.

The existing missing_config_errors_are_escaped now also checks that a non-JSON run prints nothing on stdout. cargo test -p meta after the rebase on #47: all pass.

Related

• docs: the JSON error --json callers get without a config meta#131 documents the error in the README (same branch).
• gitkb/atc#606 uses it and needs this merged first.

Task: [[tasks/harmony-2794]]

Related: gitkb/meta_project_cli#22 (project aliases in project list --json, same branch) is also needed by atc#606.

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