Legacy plugin loader pushes non-Hooks return values, corrupting plugin loading and crashing startup

Summary

opencode 1.16.2's legacy plugin loader (getLegacyPlugins in packages/opencode/src/plugin/index.ts) invokes EVERY exported function of a plugin module as a plugin and pushes its return value into the hooks array WITHOUT validating it is a Hooks object. A plugin that exports helper functions that return undefined/false (in addition to the real plugin factory) pollutes the hooks array with non-Hooks entries. This corrupts plugin loading and can crash startup without a visible load error.

The same root cause explains two crash signatures observed at startup:

• config-hook loop: (hook as any).config?.(cfg) throws Cannot read properties of undefined (reading 'config') (looped under Effect.ignore, so non-fatal but logged).
• provider state initializer (packages/opencode/src/provider/provider.ts, instanceState.make does for (const hook of plugins) { const p = hook.provider; ... }): undefined.provider throws Cannot read properties of undefined (reading 'provider'). This loop is NOT wrapped in Effect.ignore, so it aborts provider state init and crashes Provider.list.

Context

Custom plugins written as { id: <plugin>, ...hooks } legacy-style modules, or plugin modules (built with the @opencode-ai/plugin SDK) that chose named exports: the plugin factory plus adjacent helper functions. Example: a plugin module exporting isLockdownError, handleRateLimit, timerTick, and <Plugin> as four named function exports. The legacy loader treats all four as plugin factories.

Root cause detail

1. readV1Plugin(mod, "detect") returns undefined when mod.default is absent or is a function (only a record with id/server/tui keys routes to the v1 path). So any module without a record default falls through to the legacy path.
2. getLegacyPlugins(mod) iterates Object.values(mod) and calls getServerPlugin(entry) (which only checks typeof value === "function"). Every function export is treated as a plugin.
3. applyPlugin does hooks.push(await entry(input, load.options)) with no check that the returned value is a Hooks object. Helper functions that return undefined or false get pushed into the shared hooks array.
4. Later consumers index the array as if every entry were a Hooks object. The fatal one is instanceState.make: const p = hook.provider on an undefined entry throws.

Expected behavior

A plugin that returns a non-Hooks value from its module export should fail that plugin load gracefully and log a clear error, rather than polluting the hooks array and crashing a later consumer. At minimum, getLegacyPlugins / applyPlugin should filter out entries whose value is not a Hooks object.

Impact

• Crash #1 (load list: magic-context, instant-file-search, mullvad, server-start-guard, bmc-panel, speak, gk-hooks): 2x j.config + t.provider crash.
• Crash #2 (same minus bmc-panel and server-start-guard): identical 2x j.config + t.provider crash.
• Clean boot (crashing plugin removed): zero errors.

The single discriminating variable between the crashing boots and the clean boot was the plugin with the helper exports returning undefined.

Environment

• opencode 1.16.2 (WinGet install)
• @opencode-ai/plugin SDK 1.17.8
• Loader ref: tag v1.16.2 = commit 76c631d198f9ff620e15468e45f3457d50481b57