fix: use %w instead of %s for error wrapping in fmt.Errorf calls

[AdeshDeshmukh]

Description

This PR fixes 11 instances across 8 files where fmt.Errorf was using %s to format an error argument instead of %w. While the error messages read just fine either way, using %s silently breaks the error chain — callers using errors.Is() or errors.As() cannot unwrap through these errors to inspect the underlying cause.

This is a Go best practice that the rest of the codebase already follows correctly (many adjacent lines use %w properly). These were likely copy-paste oversights.

What was changed

Every fix is the same pattern: %s → %w for the error argument in a fmt.Errorf call.

Package	File	Lines	Context
pkg/lib/filesystem/unpack	core.go, skill.go, util.go	4	Wrapping getStoreForRef, GetManifest, and NewLocalRepo errors
pkg/lib/repo/local	migration.go	2	Wrapping os.RemoveAll errors during storage migration
pkg/cmd/remove	remove.go	2	Wrapping removeModelRef and oras.Resolve errors
pkg/cmd/tag	tag.go	1	Wrapping oras.Resolve error
pkg/cmd/kitimport	util.go	1	Wrapping os.WriteFile error
pkg/cmd/dev	opts.go	1	Wrapping findAvailablePort error

Additional cleanup

In pkg/lib/filesystem/unpack/util.go, the format string also had a stray trailing \n ("failed to read local storage: %s\n"), which was removed as part of the fix. Trailing newlines are unusual in Go error messages and can cause formatting issues in logs.

Verification

• go vet ./... — ✅ passes
• go build ./... — ✅ compiles
• go test ./... — ✅ 63 tests pass across 6 affected packages
• DCO sign-off included

Why this matters

Consider a caller trying to inspect the error from removeModel():

err := removeModel(ctx, opts)
if errors.Is(err, errdef.ErrNotFound) {
    // Handle not-found case
}

Before this fix, the %s verb stringifies the underlying error, so errors.Is() never matches — even though the codebase explicitly checks err == errdef.ErrNotFound in the same functions. After the fix, the error chain is preserved and unwrapping works as intended.

Checklist

• Changes are minimal and targeted — each fix is a single character change
• go vet reports no issues
• go build succeeds
• Existing tests pass (63 tests across 6 packages)
• DCO sign-off included

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Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

[AdeshDeshmukh]

Agreed that message was misleading. Updated in the latest push.