harness-pi: empty tool results are not JSON-safe and meaningful details are discarded

Finding: In @ai-sdk/harness-pi 1.0.149 (source commit e00b1b14e99b9f0fcb5e49848b26ff84613ea067), when a Pi tool_execution_end result has empty text, the translated tool-result can keep an envelope with an own details: undefined member, which a strict JSON consumer may reject; text flattening also discards native details and image content. Source: https://github.com/vercel/ai/issues/22414. This is an external report with no KFA reproduction. Reported behavior: ordinary nonempty text projects correctly, but empty text yields the envelope rather than a string, and results carrying details, image or mixed content, empty content arrays or extra envelope fields lose data or are not preserved properly (issue body and the contributor reproduction comment, https://github.com/vercel/ai/issues/22414#issuecomment-6080703258). Error status itself reportedly stays intact, and the host-result exact-value cache and native-source immutability behave as expected. The same comment says pi-session.ts builds native tool results with details: undefined, a contributing condition. Reported cause: a contributor bugfix comment says unwrapPiToolResult flattened content envelopes and returned joined text only if truthy, so empty text fell through to the envelope (https://github.com/vercel/ai/issues/22414#issuecomment-6081171472). This is contributor-asserted, not maintainer-confirmed. Proposed fix (not confirmed shipped): the issue body's diff makes text-only results without meaningful details project to a string, including empty text; envelopes with details, non-text content, empty content arrays or extra fields are preserved; absent optional details are omitted; and asPiToolResult uses null for required absent details. The reporter says regressions fail on original source and pass with the fix, and 74 focused tests pass across four adapters; full workspace typecheck is not claimed. A comment references PR #22425, but whether it merged or which release contains it is unknown from the supplied sources. The issue is closed, and closure alone does not prove a fix. Diagnosis hint: if you consume harness-pi tool-result events with a strict JSON parser and see failures on empty tool output, check whether the result object has an own details key set to undefined. Limitations: evidence comes from one reporter and associated contributor comments; no independent reproduction; no release version with the fix is identified; no documented workaround.