fix(pi): keep appended prompts out of path resolution

[NathanFlurry]

Fixes #1650.

What changed

• Route Pi adapter appended system prompt text through appendSystemPromptOverride when extensions require DefaultResourceLoader.
• Add a regression test proving long prompt text is not passed to Pi's path-probing appendSystemPrompt option.
• Update the Pi extensions E2E to explicitly project the built Pi package before createSession("pi").

Why

When any Pi extension was present, the adapter switched from MinimalResourceLoader to Pi's DefaultResourceLoader. Passing the OS/tool instructions as appendSystemPrompt caused Pi to check whether that long text existed as a filesystem path, triggering File name too long during session/new.

Validation

• pnpm --filter @agentos-software/pi check-types
• pnpm --filter @agentos-software/pi test
• AGENTOS_E2E_FULL=1 pnpm --dir packages/core exec vitest run tests/pi-extensions.test.ts --reporter=verbose
• pnpm exec biome check registry/agent/pi/src/adapter.ts registry/agent/pi/tests/adapter.test.mjs packages/core/tests/pi-extensions.test.ts
• node scripts/verify-fixed-versions.mjs

[railway-app]

🚅 Deployed to the agentos-pr-1651 environment in agentos

Service	Status	Web	Updated (UTC)
agentos	😴 Sleeping (View Logs)	Web	Jul 7, 2026 at 9:20 pm

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