fix(core): accept string items in message content arrays

[christso]

Closes #1034

Summary

agentv validate accepted message content arrays mixing inline strings with structured blocks like {type: file, value: ...}, but agentv eval run skipped the same test as "incomplete". The validator and the runtime loader disagreed on what a valid TestMessage looked like.

This PR makes the loader, prompt builder, and isTestMessage guard agree with the validator: plain string items inside a content array are treated as inline text segments alongside structured blocks.

Changes

• packages/core/src/evaluation/types.ts
  • Widen TestMessageContent to string | JsonObject | (string | JsonObject)[].
  • isTestMessage accepts content arrays whose items are strings or JSON objects.
• packages/core/src/evaluation/input-message-utils.ts
  • extractContentSegments converts string items into {type:'text',value:...} segments (drops empty strings).
• packages/core/src/evaluation/loaders/message-processor.ts
  • Both processMessages and processExpectedMessages convert string items to text segments. processMessages also surfaces them through textParts for prompt building.
• Tests
  • shorthand-expansion.test.ts: lock in that mixed string + structured-block content arrays survive expandInputShorthand.
  • message-processor.test.ts: cover the mixed-content shape end to end (resulting segments + textParts).

Red / Green UAT

Reproduction file:

description: red repro with inline string block in content array
tests:
  - id: red-inline-string-block
    criteria: Returns a short answer
    input:
      - role: user
        content:
          - |-
            Use the local file.
          - type: file
            value: /README.md

Red (origin/main):

$ agentv validate red-inline-string-block.eval.yaml
✓ red-inline-string-block.eval.yaml

$ agentv eval run red-inline-string-block.eval.yaml --test-id red-inline-string-block --dry-run
Error: Skipping incomplete test: red-inline-string-block. Missing required fields: id, input, and at least one of criteria/expected_output/assertions
Error: No tests matched the provided filters.

Green (this branch):

$ bun apps/cli/src/cli.ts eval run .tmp/agentv-repro/red-inline-string-block.eval.yaml --test-id red-inline-string-block --dry-run
...
Top performing tests:
  1. red-inline-string-block: 0.000
Results written to: .agentv/results/runs/.../index.jsonl

The generated input.md shows the inline string and the resolved file content interleaved correctly:

@[user]:
Use the local file.

<file path="README.md">
# AgentV
...
</file>

Test plan

• bun run typecheck
• bun run test (1976 tests pass)
• bunx prek run --all-files --hook-stage pre-push (Build / Typecheck / Lint / Test / Validate eval YAML files all green)
• Manual red/green eval run on the reproduction file from issue agentv eval run skips valid eval when message content array mixes string and file blocks #1034

🤖 Generated with Claude Code

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