feat(config): set environment variables per directory with [[context]] rules

[timvw]

Closes #138.

Path patterns can already read {.env.X}, but supplying the value meant exporting it per command or wiring up direnv. This adds includeIf-style rules that bind variables to a directory tree instead:

[[context]]
when_path = "~/dev/repos/work"
env = { WT_CATEGORY = "work" }

wt clone acme/api      # ~/dev/repos/work/acme/api/main, no export needed

Semantics

Matching is a path prefix, not a glob — filepath.Match has no **, and a glob library would be a new dependency for a module with 8 direct ones. Paths are resolved (~ expanded, absolute, symlinks followed) before comparison, and compared case-insensitively on macOS and Windows. ~/dev/work does not match ~/dev/workshop.

Composition: every matching rule applies, later rules winning per variable — the same way git config treats repeated keys. A broad rule can set a default that a narrower one overrides.

Which path is matched differs by command, and in neither case is it the rendered destination, so nothing is circular:

Command	Matched against
wt create, wt co, wt pr, wt mr, wt migrate	the repository's main checkout
wt clone	the working directory

Matching the main checkout rather than the cwd means every linked worktree of a repo resolves to the same rule, even when worktree_root puts them in a completely different tree. For wt clone no repo exists yet, so the cwd is the only signal available.

Rules are rendering-only. They are merged underneath os.Environ() into the template's env map and never exported. An actual export still wins — including an empty one, so WT_CATEGORY= wt clone still collapses the segment — and hooks see an unchanged environment.

Source: user config file only. A repo's .wt.toml is committed by someone else; letting it inject variables would let a cloned repository redirect where its own worktrees land. Reading rules from git config needs multi-value support in the wt.* parser (cmd/config.go:153 flattens into a map[string]string, so a rule with two env entries would collide) — left as a follow-up on #138.

Notes

• docs/configuration.md now leads with [[context]]; the direnv recipe added in docs: add direnv recipe for per-directory categories #143 is kept as a "without wt configuration" subsection.
• wt config init emits a commented [[context]] example.
• 16 new tests in cmd/context_test.go cover matching (including the workshop/work sibling case), per-variable composition, export precedence, symlink resolution, nonexistent paths, ~ expansion, the config-file/.wt.toml split, and both call sites.

[codecov]

Codecov Report

❌ Patch coverage is 88.46154% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 43.78%. Comparing base (ecd4f2c) to head (ddf2c6d).

Files with missing lines	Patch %	Lines
cmd/context.go	88.88%	5 Missing ⚠️
cmd/clone_path.go	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #145      +/-   ##
==========================================
+ Coverage   43.06%   43.78%   +0.72%     
==========================================
  Files          34       35       +1     
  Lines        3597     3647      +50     
==========================================
+ Hits         1549     1597      +48     
- Misses       2048     2050       +2     

Files with missing lines	Coverage Δ
cmd/config.go	88.77% <100.00%> (+0.12%)	⬆️
cmd/worktree_path.go	61.06% <100.00%> (ø)
cmd/clone_path.go	69.04% <75.00%> (-0.19%)	⬇️
cmd/context.go	88.88% <88.88%> (ø)

... and 2 files with indirect coverage changes

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