e: multi-line pattern support for after/before/replace

[c3d4r]

Problem

The e after, e before, and e replace commands only match single-line patterns. Real-world code patterns frequently span multiple lines:

// Can't match this with `e after`
type WindowSizeMsg struct {
    Width  int
    Height int
}

In our evaluation, both agents (Runs C and D) independently identified this as the main reason they preferred the built-in Edit tool over e for code modifications. When e after failed on a multi-line pattern, they had to fall back to e append with a line number, which is fragile (line numbers shift after edits).

Proposal

Support multi-line patterns in content-addressed commands:

# Match a multi-line block
e after file.go $'Height int\n}' 'new content'

# Or with --stdin for complex patterns
echo 'type WindowSizeMsg struct {
    Width  int
    Height int
}' | e --stdin replace file.go - 'replacement'

Design options

1. Newline literals in patterns — interpret \n in pattern strings
2. Multi-line stdin patterns — use --stdin to read the match pattern too (needs a separator or second flag)
3. Heredoc-style — e after file.go <<'MATCH' <<'TEXT'

Option 1 is simplest and covers most cases. Option 2 handles arbitrary content.

Impact

Without this, e cannot compete with the built-in Edit tool for real-world code changes. The Edit tool's exact-string-match approach handles multi-line blocks naturally and was unanimously preferred by the evaluation agents.