MGS1029: source glob reaches into a pruned directory

A target declares a source pattern whose directory prefix passes through a tree magus prunes, so it matches nothing and keys nothing.

[MGS1029] docs: source glob "proto/gen/*.binpb" can never match: the expansion
walk prunes "gen"

Why

The walk that builds a cache key skips four directory names wholesale, from project.IgnoreDirs:

Pruning them is what keeps a broad pattern honest. A project declaring **/*.js means its own sources; without the prune it would hash every file in node_modules and key on a dependency tree nobody edits.

The cost is that a pattern aimed at one of those directories can never match. It is not an error at authoring time and not an error at run time - the glob is well-formed, it simply describes files the walk will not visit. The target then replays from cache while the files it named change underneath it.

This is the input-side twin of MGS1014, which catches a declared output that no run produces. Same shape: a declaration and reality quietly disconnected.

What it is not

An exact path is fine, and is not reported:

ctx.readsFiles(workspace.file("proto/gen/descriptor.binpb"));   // works
ctx.readsFiles(workspace.file("proto/gen/*.binpb"));            // MGS1029

A wildcard-free declaration names one file, so magus resolves it by stat rather than by the walk. It reaches the cache key normally even from inside a pruned tree. Only a pattern is unmatchable, because only a pattern could expand to swallow a dependency tree.

Fix

Name the file exactly, if you meant one file:

ctx.readsFiles(workspace.file("proto/gen/descriptor.binpb"));

Or declare the real sources instead of the generated artifact. A generated tree is downstream of something you own, and keying on that something is both narrower and more honest:

// not proto/gen/*.binpb - the schema the descriptor is built from
ctx.readsFiles(workspace.file("proto/magus/**/*.proto"));

If the files genuinely live under a pruned name and are genuinely sources, rename the directory. gen, vendor, node_modules and target carry a meaning across every magus workspace, and a hand-written source tree under one of those names will surprise more than this check.

Confirming the fix

Ask what the cache key actually contains:

magus describe target <target> <project> --cache --inputs

Every hashed file appears as a src: line. If a file you declared is missing from that list, it is not in the key, whatever describe target reports under sources:.