fix(edit): enforced seen-line guard on write tags

[roboomp]

Repro

A write of alpha\nbeta\ngamma returns [seen-probe.txt#B6C1]; without reading, PUT 2.=2: with +BETA against that tag used to apply and change beta to BETA instead of revealing line 2. Run cd packages/coding-agent && bun test test/write-hashline-header.test.ts: the new contract case fails against the unfixed addon.

Cause

maybeWriteSnapshotHeader in packages/coding-agent/src/tools/write-content.ts records the write tag with an empty seen-line set; assert_seen_lines in crates/pi-edit/src/modes/hashline/patcher.rs returned early for that set, conflating no lines seen with no provenance known.

Fix

• Treat Some(empty) as nothing seen in assert_seen_lines, preserving the None early return and the inline reveal/retry path.
• Update packages/coding-agent/test/write-hashline-header.test.ts to assert rejection, unchanged file, and success after the reveal; retain an unanchored append through a local:// write tag.
• Update the permission-denied fallback write-to-edit test to retry after the anchor reveal; document the user-visible guard in the coding-agent changelog.

Verification

bun test test/sdk-file-write-fallback-extension.test.ts test/write-hashline-header.test.ts passed (13/13) with the rebuilt native addon; the four affected edit suites passed (20/20), and a manual write-tag edit returned never displayed with 2:beta revealed and the file unchanged. The contract test failed against the old addon (1 failure). Skipped pre-publish gates (bun run fix, bun check, bun run test) because the same check and full-suite commands fail on a clean origin/main archive: bun check fails compiling zstd-sys in the shared Rust cache with Operation not permitted; bun run test fails at packages/utils/test/dirs-xdg.test.ts:82 with EACCES creating /srv/agent-home/.omp-dirs-xdg-*. The worktree exhibits the same failures; the diff-related write-to-edit test failure from the first gate run was corrected and its focused suite passed.

Fixes #15666

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-14T04:30:19.814830Z	a9b2b1d	PR opened

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