[kooksee]

Summary

Removes three unmaintained/problematic external dependencies and fixes long-standing bugs in environment variable substitution:

• github.com/a8m/envsubst → replaced by a built-in expander (env/expand.go), fixing default-value and digit-key resolution bugs.
• github.com/ettle/strcase (upstream unmaintained) → vendored into internal/strcase with its MIT license preserved.
• github.com/iancoleman/strcase → removed; the codegen plugin now uses the vendored internal/strcase.

Changes

envsubst removal & substitution fixes (5c29c29)

• Fix ${VAR:default} silently resolving to empty. envsubst implements bash parameter expansion, where the single-colon form is a substring offset, not a default value. ${PORT:8080} with PORT unset resolved to an empty string, so numeric defaults like port: ${PORT:8080} never applied (loaded as 0).
• Fix keys containing digits failing to resolve. keyHandler renames keys at digit-to-uppercase boundaries on env.Set/Reload (T2HOST is stored as T2_HOST, SHA256SUM as SHA256_SUM), while substitution looked up the raw name only, so declared values were never found.
• New substitution semantics (env/expand.go):
  • ${NAME} / $NAME — env value, empty when unset
  • ${NAME:default} / ${NAME:-default} — default when unset or empty; everything after the first : is the default (inner colons kept, surrounding quotes stripped)
  • declared patch_envs values keep priority over inline defaults (existing behavior preserved)

env key-resolution hardening (b9072ef)

• Unified 3-candidate lookup (raw name → keyHandler(name) → keyHandler(ToUpper(name))) shared by Expand, Get/getVal and Lookup, so lowercase references of renamed digit keys resolve too (${sha256sum} finds SHA256_SUM).
• Delete unsets every stored spelling of a key, so variables saved under a renamed key are actually removed.
• New typed getters GetBoolOr / GetIntOr / GetFloatOr — explicit defaults on unset/empty/parse-error instead of -1/false sentinels.
• Documented Reload() blast radius: it rewrites the whole process environment in place; warning added to doc comment and READMEs.
• Fixed documented-but-unimplemented ${env.VAR} syntax in config docs (real syntax is the CEL env("VAR") function).

resty lint fix (0f496e3)

• Drop deprecated net.Dialer.DualStack in component/resty (staticcheck SA1019, pre-existing CI lint failure).

strcase vendoring (a54c794)

• Copy the used subset of github.com/ettle/strcase v0.2.0 into internal/strcase (caser, split, convert, initialisms, unicode helpers) with upstream tests kept as the behavioral spec; MIT license text and copyright preserved in internal/strcase/LICENSE.
• Only importer env/util.go switched to the internal path; go mod tidy drops the dependency. No behavioral change (key normalization verified unchanged).

iancoleman/strcase removal (4f18b58)

• cmds/protoc-gen-go-errors2 and the protoutils test only used ToCamel/ToSnake; switched to the vendored internal/strcase (ToPascal/ToSnake). Output is identical for conventional proto naming; names with digits or acronyms now produce more idiomatic Go (APIKey -> ApiKey instead of Apikey).

Also carries refactor: adopt modern Go stdlib APIs across packages (b82d7e2): mechanical reflect.TypeOf → reflect.TypeFor modernization committed on this branch.

Supersedes #65.

Behavior changes

• ${VAR:default} now applies the default when the variable is unset or empty (previously silently empty). Bash advanced expansions (:?, #len, substring, // replace) are no longer supported by env.Expand — none were used in the repo or documented.
• Get/Lookup/Delete resolve additional key spellings (raw name first); keys stored under exactly one spelling keep their values, so existing callers are unaffected unless a raw and a normalized key coexist.
• Deliberately not changed: keyHandler's renaming itself (case-asymmetric) — deferred to v3.

Testing

• Vendored upstream strcase suite passes (go test ./internal/strcase/)
• env/expand_test.go (24 cases), env/api_test.go (raw fallback, typed getters, LoadFiles, Expand×Reload), config/expand_test.go (4 end-to-end regressions)
• go test -race ./env/ ./config/ and full suite go test ./... pass; golden config tests unchanged
• go vet clean; golangci-lint run repo-wide: 0 issues