fix: finalize async-tar Builder on upload error to avoid worker-thread panic - #786

Fixes #783
Routing-Key: inbox-route/I_kwDOSUhdos8AAAABI_XyLQ

Problem

min activate streams the project directory to the daemon as a tar+zstd archive built on a background task (crates/minimal/src/file_upload.rs). The tar Builder was finalized with into_inner() only on the success path.

When the upload channel closes mid-stream, the tokio::io::copy in stream_tar_zstd returns an error and the function returns early, dropping the duplex reader. The background build task's next write to the pipe then fails, so add_dir_entries returns early via ? — dropping the Builder without finalizing it. async-tar 0.6.1's Builder::drop panics in that case (Builder dropped without finalizing; call finish() or into_inner(), builder.rs:671), crashing a tokio worker thread on top of the real error the user already saw.

Fix

Extract the archive construction into build_tar_zstd, which always calls into_inner() to finalize the Builder — even when adding entries failed — before propagating the original error. Because the builder is finalized on every path, its Drop guard never fires, so a mid-stream channel close now surfaces as only the clean Failed to upload project files: ... channel closed error with no panic.

The change is confined to the sender-side upload path; no receiver-side change was needed. Feature area confirmed against the tarball session-population work in this repo (informed by #423).

A regression test (file_upload::tests::build_surfaces_error_when_writer_fails_mid_stream) drives build_tar_zstd with a writer that fails part-way through the (incompressible) stream and asserts the failure surfaces as an Err rather than a panic.

Verification

• cargo fmt --all --check --manifest-path target/Cargo.toml — clean, no drift.
• cargo clippy --workspace --manifest-path target/Cargo.toml -- -D warnings — finished, no warnings.
• cargo build --workspace --manifest-path target/Cargo.toml — Finished in 1m 19s, no errors.
• cargo test --workspace --manifest-path target/Cargo.toml — passed (exit 0); the minimal lib reports test result: ok. 6 passed; 0 failed including the new regression test.

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