fix(opencode): never place cache_control on message object in hybrid mode

[iceteaSA]

Problem

In hybrid cache mode, setMessageCacheAnchor() fell back to setWireCacheControl(message, true) when a message had empty content or only thinking/redacted_thinking blocks. That attaches cache_control to the message object, which Anthropic only permits on content blocks.

When resuming a session whose moving anchor (messages[n-2]) landed on such a message, the API rejected the request:

messages.N.cache_control: Extra inputs are not permitted  (HTTP 400)

Fix

Never anchor on the message object. In setMessageCacheAnchor():

• Return false when content is empty (instead of setting cache_control on the message).
• Exclude redacted_thinking alongside thinking when finding the last cacheable block.
• Return false when no cacheable block exists.
• Only materialize the normalized content array once an anchor target is confirmed.

Tests

Adds 2 regression tests:

• hybrid mode never sets cache_control on the message object when the n-2 anchor has no cacheable block
• hybrid mode anchors on the last non-thinking block, never the message object

All opencode tests pass (261), typecheck clean, biome clean.

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Summary by cubic

Prevents 400s in hybrid cache mode by never setting cache_control on message objects. Anchors only on valid content blocks to avoid “messages.N.cache_control: Extra inputs are not permitted”.

• Bug Fixes
  • Skip anchoring on empty content; never attach cache_control to the message.
  • Anchor only the last non-thinking/redacted_thinking block; skip when none exists.
  • Normalize content only after confirming an anchor; add regression tests for empty and mixed content.

^{Written for commit 1ba42c1. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

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