[Bug] @file attachments can load the wrong file when a filename contains a Unicode space

[PLASMA-FR]

Affected area: Coding agent and CLI — @file arguments.

The documented file-argument workflow can attach a different document from the one requested when the filename contains a Unicode space. With an existing report\u00a0draft.txt (U+00A0, non-breaking space), read-path resolution first changes the name to report draft.txt (U+0020). If that second file exists, its contents are attached. If it does not exist, resolution returns a nonexistent path despite the requested file being present.

Reproduced from source at 427ea4c72cc606ac061a14287c0c15c471eff002 (main, package version 0.9.4), on Ubuntu 24.04.4 LTS, aarch64, Node 26.8.1, npm 11.19.0, Bash 5.2.21 in a noninteractive shell. This uses the real argument parser and attachment processor with temporary text files; no daemon or model credentials are needed.

From the repository root after npm ci:

node --import tsx --input-type=module <<'JS'
import { existsSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
import { tmpdir } from 'node:os';
import { join } from 'node:path';
import { parseArgs } from './packages/coding-agent/src/cli/args.ts';
import { processFileArguments } from './packages/coding-agent/src/cli/file-processor.ts';
import { resolveReadPath } from './packages/coding-agent/src/core/tools/path-utils.ts';

const dir = mkdtempSync(join(tmpdir(), 'prime-atfile-'));
try {
  const requested = join(dir, 'report\u00a0draft.txt');
  writeFileSync(requested, 'INTENDED DOCUMENT');
  console.log('Requested exists:', existsSync(requested));
  console.log('Resolved exists:', existsSync(resolveReadPath(requested, dir)));
  writeFileSync(join(dir, 'report draft.txt'), 'DIFFERENT DOCUMENT');
  const parsed = parseArgs(['@' + requested]);
  const result = await processFileArguments(parsed.fileArgs);
  console.log(result.text.replaceAll(dir, '<tmp>'));
} finally {
  rmSync(dir, { recursive: true, force: true });
}
JS

Actual output:

Requested exists: true
Resolved exists: false
<file name="<tmp>/report draft.txt">
DIFFERENT DOCUMENT
</file>

Expected: resolution finds the existing U+00A0 filename, and the attachment contains INTENDED DOCUMENT even when the ordinary-space sibling exists.

The cause is in read-path resolution: Unicode-space normalization happens before the first existence check. History and the existing tests show that normalization and macOS screenshot fallbacks are intentional. Proposed scope, subject to maintainer invitation: give an existing literal read path precedence, retain those fallbacks when the literal path is absent, and cover both the missing-path and wrong-attachment cases, including relative and absolute paths. Add the required coding-agent changelog fragment.

Validation already run: all 16 existing tests pass with npx tsx ../../node_modules/vitest/dist/cli.js --run test/path-utils.test.ts from packages/coding-agent; an ordinary-space attachment control also passes. An approved fix would run the focused path and attachment regressions plus npm run check.

I found no matching Discussion or issue, and no open PR changes read-path resolution. The attachment-file overlap in #1980 only renames a type import. No implementation changes have been made. I would like to take this scope if maintainers invite it and approve PR submission.