[test] Add tests for server.callBackendPrompt

[github-actions]

Test Coverage Improvement: callBackendPrompt

• Package: internal/server
• Function: callBackendPrompt
• Previous coverage: 79.5%
• New coverage: 82.2%
• Complexity: High (DIFC pipeline phases, many error branches)

Why this function?

It's the most complex function with remaining gaps among the under-tested ones (most other low-coverage functions are trivial or test helpers).

Tests added

• Unlabeled response passthrough
• Collection with all-allowed items
• Collection with null messages (unexpected type error)
• Backend rejecting malformed messages
• Unlabeled response with denied DIFC evaluation (filter mode)
• Per-server ToolTimeout override
• Backend JSON-RPC error propagation

Test execution

go test ./internal/server -run TestCallBackendPrompt passes; go vet clean.

---

Generated by Test Coverage Improver

Warning

Firewall blocked 4 domains

The following domains were blocked by the firewall during workflow execution:

• example.com
• nonexistent.local
• slow.example.com
• thishostdoesnotexist12345.com

To allow these domains, add them to the network.allowed list in your workflow frontmatter:

network:
  allowed:
    - defaults
    - "example.com"
    - "nonexistent.local"
    - "slow.example.com"
    - "thishostdoesnotexist12345.com"

See Network Configuration for more information.

Generated by Test Coverage Improver · copilot · auto · 42.5 AIC · ⊞ 10.7K · ◷