fix: send valid tool schemas and non-empty reasoning replay to OpenAI-compatible relays

[vastsa]

Fixes #864.

Two independent causes behind PROVIDER_ERROR against an OpenAI-compatible
relay (ps.air-outer.com + deepseek-v4-flash).

1. Read reached the relay with no required key at all.
Read, Glob, Grep, and BrowserPreview declare their canonical argument
as Type.Optional so the file_path / query alias spelling validates too;
TypeBox 1.x then omits required entirely. The OpenAI chat/completions adapter
forwards parameters verbatim (only the Anthropic adapter fills
required ?? []), so a relay that decodes the missing key into a nil slice
answered Invalid schema for function 'Read': null is not of type "array".
Neither the relay nor PI-Desktop ever emitted a literal null.

The schema is now normalised in rebuildToolCatalog(), the single origin of
every tool, so the session agent and a delegated Task run send the same
declaration. An absent required already means "nothing is required", so
writing an empty array changes no tool's accepted arguments.

2. The non-empty reasoning replay never reached the wire.
The 0.86.1 patch taught convertMessages to fill a documented placeholder for
relays that reject an empty reasoning echo, but pi-ai rebuilds compat from an
explicit allowlist in getCompat, so the flag provider-binding puts on a
relayed DeepSeek model was dropped. The fill silently degraded to an empty
string, which strict relays reject with The reasoning_content in the thinking mode must be passed back to the API. The opt-in now passes through getCompat
and is declared on OpenAICompletionsCompat. No endpoint can be auto-detected
as requiring a non-empty echo, so it stays an explicit model.compat opt-in.

Validation

Base: 6ad892d806af

• pnpm build:js — passed (including apps/desktop)
• pnpm --filter @pi-desktop/desktop typecheck — passed
• pnpm -r --if-present test — passed
• pnpm lint — passed
• node scripts/check-architecture.mjs — passed (2 new files, 40 / 52 LOC)
• pnpm check:pr-base — passed
• Rust untouched

Each new test was confirmed to fail before its fix:

• Read.required absent: Read: expected { Object (type, properties) } to match object { type: 'object', required: [] } on both the session and the
  delegate path
• getCompat passthrough removed: expected '' to be '[reasoning not retained for this turn]'

The reasoning test drives a real request through buildProviderModel → pi-ai
getCompat → the adapter and asserts the captured outbound body, because the
existing backfill test hands a hand-built compat straight to
convertMessages and therefore cannot see a dropped flag.

Not run: verify:ui:* E2E. These are wire-format defects proven at the adapter
boundary — the reasoning test asserts the actual request body — and the UI E2E
suites require an explicit request per repository policy.

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