tape-fold: don't synthesize tool results for aborted assistant messages

[ReganBell]

Problem

When a user aborts a turn while the model is mid-stream, pi commits the partial assistant message with stopReason: "aborted". If the abort landed after a complete toolCall block, that message contains a tool call that never executed and has no tool result.

The tape fold treated that call as dangling: tapeNeedsInterruptHeal flagged it, an interrupt event was appended, and healDanglingCalls synthesized an INTERRUPTED_TOOL_RESULT for it. But pi's transformMessages drops aborted/errored assistant messages entirely when building the provider request, while keeping every toolResult message. The healed result therefore reached the provider as a tool_result block with no corresponding tool_use in the previous message:

Model provider API error (invalid_request_error): messages.N.content.1:
unexpected `tool_use_id` found in `tool_result` blocks: toolu_… Each
`tool_result` block must have a corresponding `tool_use` block in the
previous message.

Every subsequent step re-serves the same fold, so the session is permanently wedged: each turn fails with the same 400.

Fix

• healDanglingCalls skips assistant messages with stopReason "aborted"/"error" when collecting dangling calls. Those messages are never replayed, so their calls need no results — and synthesizing one is what poisons the request.
• lintFold no longer counts such messages' calls as open. A toolResult answering one now lints as a problem, so a fold that would orphan a result on the wire falls back to entry-based replay instead of being served.

The interrupted-result heal is unchanged for the case it exists for: a restart mid tool execution, where the assistant message completed normally (stopReason: "toolUse") and is replayed.

Testing

• New test: an aborted assistant's dangling call is not healed and the fold lints clean.
• New test: lintFold rejects a fold where a toolResult answers an aborted assistant's call.
• node --test test/tape-fold.test.ts — 26/26 pass; tsc --noEmit and eslint clean.

Reproduced against a live session: abort a turn while the model is streaming a tool call, then send another message — before this fix every subsequent turn 400s with the error above.

🤖 Generated with Claude Code

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