Link shell library standards

CONTRIBUTING.md

@@ -2,6 +2,11 @@
 
 Thank you for improving this project.
 
+For coding and documentation standards, see [STANDARDS.md](STANDARDS.md). This
+repository inherits Base's shell-library standards, including the convention
+that each sourceable shell library remains a single file at its library
+boundary.
+
 ## Workflow
 
 1. Create or choose a GitHub issue before starting implementation work.

STANDARDS.md

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+# base-bash-libs Standards
+
+`base-bash-libs` inherits the Base shell standards as its upstream policy. See
+[Base Standards](https://github.com/basefoundry/base/blob/master/STANDARDS.md),
+especially the
+[single-file library boundary](https://github.com/basefoundry/base/blob/master/STANDARDS.md#single-file-library-boundary)
+guidance.
+
+## Shell Library Shape
+
+Each public sourceable Bash library in this repository should remain a single
+physical `.sh` file at its library boundary:
+
+- `lib/bash/std/lib_std.sh`
+- `lib/bash/file/lib_file.sh`
+- `lib/bash/git/lib_git.sh`
+
+Do not split one library into internal concern files such as separate logging,
+path, string, prompt, or command-runner fragments. That kind of split adds a
+source-order and import graph for callers without improving the public library
+contract.
+
+A new library file is appropriate when the repository adds a distinct reusable
+library boundary, such as the existing `file` and `git` libraries. Large
+libraries should stay navigable through section ordering, consistent function
+prefixes, README coverage, and focused tests rather than a shell module loader
+or chained source fragments.