fix: flush stdout before process.exit() to prevent pipe truncation

[vystrcild]

Summary

When mcpc JSON output exceeds 64KB and stdout is piped (e.g. mcpc ... --json | jq), the output is silently truncated at exactly 65,536 bytes, producing broken JSON that downstream parsers can't read.

Root cause

src/cli/index.ts line 232 calls process.exit(0) after command execution. When stdout is a pipe, Node.js uses async I/O — console.log() buffers data internally and flushes it asynchronously. process.exit() terminates the process before the buffer is fully written to the pipe, discarding any data beyond the 64KB kernel pipe buffer.

When stdout is a file or TTY, Node.js uses synchronous writeSync(), so all data is written before process.exit() runs — which is why mcpc ... --json > file.json always works.

Reproduction

# Pipe: truncated at exactly 64KB
mcpc @apify tools-call get-actor-output datasetId:="<large>" limit:=25 --json 2>/dev/null | wc -c
# → 65536

# File redirect: complete output
mcpc @apify tools-call get-actor-output datasetId:="<large>" limit:=25 --json > /tmp/out.json 2>/dev/null && wc -c /tmp/out.json
# → 118166

# jq fails with broken JSON
mcpc ... --json | jq '.structuredContent.items'
# → jq: parse error: Unfinished string at EOF at line 194, column 22

Fix

Wait for stdout to fully drain before calling process.exit(0). The exit itself is still needed (MCP SDK's StdioClientTransport keeps the event loop alive), but now it only fires after all buffered data has been flushed.

Verified

# After fix — pipe returns complete output
mcpc ... --json 2>/dev/null | wc -c
# → 118166 ✓

# jq parses correctly
mcpc ... --json | jq '.structuredContent | {totalItemCount, count: (.items | length)}'
# → {"totalItemCount": 25, "count": 25} ✓

# File redirect still works, process exits cleanly (no hang)

Test plan

• Pipe output >64KB through jq — should parse without errors
• File redirect — should produce identical byte count as pipe
• Process should exit cleanly (no hanging from MCP SDK handles)
• Small outputs (<64KB) should still work correctly through pipes

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