fix(claudecode): a message's content is a string or a list, not only a list

[pedromvgomes]

claudecode's decoder models message.content as a list of content blocks. Claude Code also emits it as a bare string, and json.Unmarshal returns an error for the shape it does not model. Decode returns that error, so one such line fails the entire run:

provider unavailable: claude-code emitted an unreadable event:
json: cannot unmarshal string into Go struct field .message.content of type []struct{...}

The failure surfaces as ErrProviderUnavailable — a stream that was working, reported as the CLI being unreachable, which invites a retry that fails identically.

Why the existing tolerance didn't cover it

Decode's doc says a line whose type this package does not model "is not a reason to fail a run that is working". That tolerance is keyed on the event type. A known type carrying a polymorphic field falls straight through it and reaches the json.Unmarshal error return at the top of the function.

The package already knows this exact polymorphism: toolResultText accepts string-or-blocks for a tool result's own content, and streamEvent's doc comment explains why. The same shape occurs one level up, on the message itself.

The change

message.content is decoded through a type accepting either shape, and neither — a null content leaves both fields zero rather than failing a line carrying no message body.

• assistant, string form — the answer itself, so it surfaces as an EventKindText event rather than being dropped.
• user, string form — the prompt echoed rather than a tool answering, so it yields the zero event, as an unmodelled line does.
• block form — unchanged, with a test pinning it, since a decoder that accepted the string by giving up on blocks would lose every tool result.

How it was found

agtk memory curate died mid-run against v0.3.0. The store was left untouched, but the run was lost. Reproduced hermetically through agentictest.Fake, with no model call:

`{"type":"user","message":{"role":"user","content":"resuming"}}` + "\n" + resultEnvelope

Each new test was confirmed to fail before the change. Verified downstream by pointing agentic-toolkit at this branch with a replace directive: the failing case passes, and the directive was dropped again rather than committed.

Impact

claudecode is the only provider that can perform a real curation run, so on v0.3.0 this breaks agtk memory curate on the default provider whenever such a line appears.

[github-actions]

bulwark

• ✅ scan — no findings

• ✅ coverage — go: 82.1% (baseline 82.0%); go patch: 85.7% (12/14 new lines; baseline 82.0%)

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