Editing and repair

Editing reliably is the core of a coding agent. Veyyon’s default edit surface is hashline: numbered lines from read/grep, snapshot tags, and edit with SWAP/DEL/INS operations.

For design background see Edits that land the first time and The hashline edit engine.

Why this matters

Models often emit slightly wrong tool JSON or stale line anchors. Hashline detects stale [path#TAG] tags and returns recovery hints. General schema repair runs on all tool calls before validation — see Repair overview.

Write path vs edit path

Path	Applier	Role
`edit`	`@veyyon/hashline` (default)	Surgical edits via snapshot tags and hashline ops
`write`	Whole-file writer	Create or overwrite files; mints new snapshot tags in hashline mode
`apply_patch` / `patch` / `replace`	Mode-specific parsers	Compatibility modes via `edit.mode`

There is one hashline edit applier for anchored edits; write is intentionally separate for whole-file creation. Both honor the same approval and sandbox policy.

Tools

Tool	What the model sends	Use for
`edit`	Hashline `input` (default) or mode-specific payload	Surgical edits
`write`	`path` + full `content`	New files or full rewrites
`apply_patch`	V4A envelope	When `edit.mode: apply_patch`

Set edit.mode to hashline, apply_patch, patch, or replace in config.yml, or PI_EDIT_VARIANT for one-shot overrides.

Hashline workflow

read (or grep) returns [relative/path#TAG] and LINE:text rows.
Model calls edit with sections anchored on the same TAG.
On success, output includes a fresh [path#NEW_TAG] and a compact diff.

write strips pasted hashline prefixes when appropriate and can mint new tags after whole-file writes.

Safety

Edits honor approval mode and sandbox roots like bash. Denied tools are removed from the model’s tool list via disallowed_tools / plan mode.

Spec — not shipped: a single V4A applier that routes every mutation through a make_update_patch envelope. Veyyon uses hashline as the primary path; apply_patch is a compatibility mode.