opencode-legacy-patch

Restores the legacy UI of OpenCode Desktop (Windows) by patching the one-line "sunset date" that OpenCode forced on 2026-09-14 to push everyone onto the new UI.

• Method: same-length binary patch over the installed app's app.asar (no recompiling, no toolchain, no third-party binaries).
• Tested on: OpenCode Desktop 1.18.35 (Electron 42), Windows, 2026-10-07.
• Works with: 1.18.34 and 1.18.35 (same literal). The script searches for the pattern dynamically, so it also works on future versions as long as upstream keeps the constant.

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Quick start

Script: patch-legacy.ps1

# 1) Patch (idempotent; works with the app open or closed)
& ".\patch-legacy.ps1"

# 2) Show status (touches nothing)
& ".\patch-legacy.ps1" -Mode status

# 3) Back to 100% official state (close the app first)
& ".\patch-legacy.ps1" -Mode restore

After patching: restart OpenCode. If your newLayoutDesigns preference was already forced to true (the normal case after the sunset), the old-interface toggle appears in Settings → enable it. With an eligible profile and an undefined preference, the legacy UI comes up directly without touching anything.

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What it does exactly

1. Sunset patch in app.asar

In packages/app/src/context/settings.tsx (compiled inside the asar):

const oldInterfaceSunset = new Date(2026, 8, 14);   // official
const oldInterfaceSunset = new Date(2099, 8, 14);   // patched

• The literal is searched dynamically; the script requires exactly 1 occurrence (if upstream changes it, the script aborts without touching anything).
• Same-length replacement (2026 → 2099, 4→4 chars): the asar header only stores file sizes, not hashes → the asar stays valid after writing.
• Post-write verification re-reads the file (2026×0, 2099×1).

Why it works: the UI is decided by resolveNewLayoutDesigns(retired, preference, fallback) = retired ? true : (preference ?? fallback). With retired=false (date in the future), the user's preference wins and, if it is undefined, the fallback legacyNewLayoutDesignsDefault = false applies for eligible profiles → legacy UI by default.

2. Updater neutralization

The Electron updater schedules void updater.start() + a check() every 10 minutes in packages/desktop/src/main/index.ts (autoDownload=false, but it downloads automatically when a newer version exists). If left alive, it would download a new version and, on "restart to update", restore the official asar and silently wipe the patch.

Fix: rewrite resources\app-update.yml (outside the asar, not covered by Authenticode) to point at a nonexistent repo → every check ends in HttpError: 404 → silent error state (error dialogs only open from the menu/IPC). Evidence after the restart:

updater state changed { from: 'checking', to: 'error' }
Error: HttpError: 404

Result: OpenCode frozen on 1.18.35 until you decide to update.

3. Backup + rollback

The first run creates:

%LOCALAPPDATA%\Temp\opencode\legacy-backup-<timestamp>\
    app.asar.bak
    app-update.yml.bak

-Mode restore reverts both files (it never overwrites a backup with an already-patched asar: the first backup is kept as the true original).

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Verification performed (2026-10-07)

Check	Result
Version	app starting { version: '1.18.35' } after relaunch ✅
Literal in asar (1.18.35)	new Date(2026, 8, 14) ×1 (confirmed before patching) ✅
After patching	2026×0, 2099×1 ✅
Hot patch	wrote the asar with the app running → allowed by Windows ✅
Updater	silent 404, no downloads or dialogs ✅
opencode.settings	oldLayoutEligible: true (toggle available) ✅
Renderer store (default.dat)	showCustomAgents: true, layoutTransitionEligible: true; newLayoutDesigns false after the toggle ✅
Legacy UI	active and persistent ✅

Safety analysis of the approach:

• Electron fuses: embedded_asar_integrity_validation defaults to 0 in Electron 42 and electron-builder.config.ts configures no fuses → no asar integrity validation.
• Authenticode: signs only OpenCode.exe (untouched) → no SmartScreen or execution impact.
• Code cache: V8 validates source content → it recompiles on its own; no need to clear Code Cache.

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Updating in the future (workflow)

# 1. Close OpenCode and go back to official
& ".\patch-legacy.ps1" -Mode restore

# 2. Open OpenCode → Settings → Check for updates → restart

# 3. Patch again
& ".\patch-legacy.ps1"
# If the literal no longer exists (upstream change), the script detects it and touches nothing.

# 4. Restart → Settings → flip the legacy UI toggle if needed

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Known limitations and risks

1. Frozen updates: while the updater is neutralized, no official bugfixes arrive. Update manually with the workflow above.
2. Upstream literal: if new Date(2026, 8, 14) disappears or changes format, the script fails safe (fail-closed) and needs revisiting.
3. Future integrity fuse: if a release enables embedded_asar_integrity_validation, the app would not boot with the patched asar → run -Mode restore.
4. A 1-line patch, not a fork: it does not replace the UI code; it only stops OpenCode from forcing the new one. The legacy UI is the legacy code upstream still ships.

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Background

• The 2026-09-14 sunset (oldInterfaceSunset) forced newLayoutDesigns=true on every profile → the previous workaround (default.dat → false) stopped working.
• Issue: anomalyco/opencode#38230 (public 👍 vote and comment).
• Community fork kuznecov-anatoliy/opencode-old-interface: analyzed and rejected (actual base is upstream v1.18.30, 3 minor patches, unsigned binaries).
• Build from source (plan C): rejected for cost (bun + toolchain + maintenance).
• Plan D (this repo): patch on top of the installed app → 5 minutes, reversible.

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Files

File	Description
patch-legacy.ps1	Script with patch (default) / restore / status modes
README.md	This document

License

MIT — use/share at your discretion.