Add --preserve for surgical, formatting-preserving json/yaml edits

[machado144]

What

Adds a --preserve (-P) flag to json/yaml set and del. Instead of the default decode → mutate → re-encode round-trip (which drops comments, reorders keys, re-indents, and rewrites quoting), --preserve performs a byte-level surgical edit: only the targeted node changes and everything else stays byte-for-byte identical — comments and their column alignment, key order, quoting style, indentation, and blank lines.

Motivation: bumping e.g. .image.tag in a hand-maintained Helm values.yaml shouldn't reformat the whole file.

How

• YAML — locate the target via the yaml.Node source line/column and splice the new value into the original bytes. Every splice is re-parsed and validated against the intended value; on any mismatch (e.g. a type-ambiguous plain-numeric edit) it falls back to the safe re-encode path, so a surgical edit can never corrupt or mis-edit the file.
• JSON — splice the exact value span. set can also insert a new key into an existing object, formatting-matched to its siblings (mirrors comma/newline separator and colon spacing). del removes the entry plus one adjacent comma.
• Atomic writes — in-place writes go through temp file + fsync + rename, preserving the original file's permission bits. A crash mid-write can't truncate the file.
• toml/csv return a clear error in preserve mode.

Compatibility

Default behavior is unchanged; --preserve is strictly opt-in.

Examples

# Edit existing value — only this line changes, comments/alignment kept
pipekit yaml set values.yaml --path '.image.tag' --value 'v2.0.0' --in-place --preserve

# Insert a new key, formatting-matched
pipekit json set config.json --path '.newKey' --json-value '{"on":true}' --in-place --preserve

# Delete a key, keeping the rest intact
pipekit json del config.json --path '.legacy' --in-place --preserve

Tests

• 29 service tests, including byte-for-byte YAML set/del assertions and JSON insert cases.
• 4 end-to-end tests (preserve set, del, key insert, file-mode retention).
• Full suite (243 tests) green, go vet clean.