fix: strip Anthropic params from 3P resume paths (#479)

* fix: strip Anthropic-specific params from 3P provider paths

Three silent failure modes affecting all third-party provider users:

1. Thinking blocks serialized as <thinking> text corrupt multi-turn
   context — strip them instead of converting to raw text tags.

2. Unknown models fall through to 200k context window default, so
   auto-compact never triggers — use conservative 8k for unknown
   3P models with a warning log.

3. Session resume with thinking blocks causes 400 or context corruption
   on 3P providers — strip thinking/redacted_thinking content blocks
   from deserialized messages when resuming against a non-Anthropic
   provider.

Addresses findings 2, 3, and 5 from #248.

* test: align resume stripping expectation with orphan-thinking filter

* test: isolate provider env in conversation recovery tests

* test: move provider-sensitive resume coverage behind module mocks

* test: trim extra blank lines in conversation recovery test

Keep the focused provider-resume test diff clean so the regression branch stays easy to review.

Co-Authored-By: Claude Opus 4.6 <noreply@openclaude.dev>

---------

Co-authored-by: Claude Opus 4.6 <noreply@openclaude.dev>

src/utils/conversationRecovery.test.ts

@@ -13,6 +13,7 @@ const originalSimple = process.env.CLAUDE_CODE_SIMPLE
 const sessionId = '00000000-0000-4000-8000-000000001999'
 const ts = '2026-04-02T00:00:00.000Z'
 
+
 function id(n: number): string {
   return `00000000-0000-4000-8000-${String(n).padStart(12, '0')}`
 }
@@ -76,4 +77,3 @@ test('loadConversationForResume rejects oversized reconstructed transcripts', as
     'Reconstructed transcript is too large to resume safely',
   )
 })
-