command-center/agent/managed-skills/line-edit-anchor-discipline/SKILL.md

name, description

name	description
line-edit-anchor-discipline	Avoid the recurring edit-tool line-op traps: empty PUT deletes lines, PUT ranges swallowing multi-line block delimiters, and anchors landing mid-expression. Use whenever issuing CUT/PUT line edits on tagged files.

Line-edit anchor discipline (CUT/PUT ops on tagged files)

Five self-inflicted syntax wounds in one session (franksign, 2026-10-21) all trace to three rules.

Rules

1. An empty PUT body DELETES the targeted lines (tool warns: "Interpreted an empty PUT body as deletion"). Twice it ate a whole log entry / a closing }. For no-ops use nothing; for deletes use explicit CUT.
2. Never PUT a range whose endpoints cut through a multi-line block. If a | {-style union variant, a frontmatter --- fence, or a test(...) closer straddles the range boundary, the replacement swallows the opener/closer and strands the body. Pre-condition: line N-1 and M+1 must be block-complete. Fix-after-the-fact pattern: read the broken region raw, then PUT k.=k: to restore the single swallowed line (e.g. the missing ---, the orphaned | {, } → });).
3. Search-hit reads do not authorize PUT. A grep/folded-summary read marks lines as "never displayed"; the edit tool refuses and echoes actual content. That refusal is a free verification — re-check the echoed lines match intent, then straight-retry with the same tag.

Costly mistakes seen

• Empty PUT 7-7: deleted a just-written log entry; restoring required re-issuing the full entry text.
• PUT 6.=7 replacing timestamp+--- dropped the frontmatter close fence → lint-breaking file silently.
• PUT 10.=11 on a union type swallowed | { opening a 12-line variant → cascade of LSP "unexpected label" warnings.
• CUT of a stranded opener left its dangling .json()) behind; balance errors surface only at EOF (expected ')' but file ends) — locate by reading regions raw, not by widening the payload.

Discipline

• After any edit that reports a syntax error or a warning: read the touched region with :raw before the next op; fix the single wrong line, do not resend the block.
• "no change: byte-identical" means your anchor math is off — re-read, don't append more content.
• Prefer replacing whole coherent blocks (start line = block start, end line = block end) over edits that end mid-statement.