`edit`: not-found error claims exact whitespace matching, but matching normalizes whitespace

Description

Summary

When oldString is not found, the tool reports:

Could not find oldString in the file. It must match exactly, including whitespace, indentation, and line endings.

This contract is false. Matching actually runs a fuzzy replacer chain that normalizes whitespace/indentation before concluding "not found". The error message and the real behavior contradict each other. This is independent of any opinion about whether fuzzy matching is desirable — the message simply misstates what the tool does.

Reproduction

File:

alpha
   beta_line
gamma

1. oldString = " beta_line" (4 spaces, file has 3) → edit succeeds (whitespace normalized), so the "must match exactly" contract is already violated here.
2. oldString = "nonexistent_text_xyz" → rejected with the error text above, which claims exactness including whitespace — the same whitespace that was just normalized in case 1.

Minimal evidence: leading indentation (4sp vs 3sp), internal spacing (foo bar vs foo bar), and tab↔spaces all match via non-exact replacers (LineTrimmedReplacer / WhitespaceNormalizedReplacer in packages/opencode/src/tool/edit.ts).

Why it's a problem

Callers (models and automation) rely on the error text to decide how to correct oldString. Telling them matching is exact-when-it-isn't sends them down the wrong path (e.g. re-checking whitespace that the tool would have tolerated anyway), and misleads spec-driven tooling about when matching will fail.

Proposed fix

Rewrite the message to reflect reality:

throw new Error(
  "Could not find oldString in the file. Exact match and all fuzzy fallbacks " +
  "(whitespace/indentation/escape-tolerant) were attempted. Re-read the file and " +
  "copy the exact text (whitespace included) into oldString."
)

Related

• Companion feature request: surface which match strategy (exact vs fuzzy) was used on success.
• Fuzzy-chain family: #41872, #32559, #31785, #42908.

Environment

• opencode: 1.18.21
• OS: Windows (win32)
• Tool: built-in edit
• Confirmed via controlled probes.

Plugins

No response

OpenCode version

1.18.21

Steps to reproduce

No response

Screenshot and/or share link

No response

Operating System

Windows 10

Terminal

No response