MCP stdio audit fixes: daslib/logger + popen_argv_pipe + stdin isolation

[borisbat]

Summary

Closes the stdio-leak audit thread that started from MCP server hangs. Every byte the MCP child process writes is now contained; every byte of the parent's stdin is unreachable to children.

Changes

daslib/logger (new)

JSON Lines structured logger for daslang tools (MCP, daslang-live, etc). One JSON object per line to {get_das_root()}/logs/<name>.log with ISO 8601 UTC timestamp, level name, dotted category, message, optional fields object.

• All public API prefixed (logger_init, logger_info, logger_warning, logger_set_min_level, logger_install_hook, ...) so short verbs don't collide unqualified.
• logger_install_hook() registers a global DapiDebugAgent that diverts print() / to_log() into the log file — critical for stdio-transport processes where any accidental stdout write corrupts JSON-RPC framing. One install covers main + every new_thread worker.

src/builtin/module_builtin_fio.cpp

• Add iso8601_now() builtin (UTC, ms precision, ISO 8601). Used by daslib/logger; also generally useful.
• Add popen_argv_pipe() builtin — bidirectional subprocess pipes (writable stdin + readable stdout). Same shell-bypass semantics as popen_argv.
• Harden popen_argv: explicitly isolate child stdin from parent. Windows: open NUL for read, pass as STARTUPINFO.hStdInput. Linux: open /dev/null, dup2(STDIN_FILENO) in child. Prevents a child from silently consuming bytes intended for the parent's JSON-RPC input.

utils/mcp/* (MCP migration)

• main.das + protocol.das: replace bespoke log_open/log_write/log_path infrastructure with daslib/logger. Dotted categories (mcp / mcp.req / mcp.res / mcp.tool / mcp.live / mcp.heap).
• tools/live.das: replace two system() calls (powershell launcher, chmod+sh wrapper) with run_and_capture / popen_argv. system() inherited MCP's stdio; any launcher chatter (PowerShell errors, COM messages) would corrupt JSON-RPC. Output now captured + logged.

daslib/command_line.das

• Add missing module command_line shared public declaration. Without it, daslang's AOT codegen emitted only an empty stub for the module, triggering error[50101] hash desync when anything required it under AOT. This unblocks AOT for any future test/utility that uses get_das_exe.

Tests

• tests/daslib/test_logger.das — 6 [test] / 12 subtests: JSON Lines write, level filter, dotted-category prefix override, JSON escaping + round-trip, fields serialization, no-op when unconfigured.
• tests/mcp/test_mcp_jsonrpc.das — spawns daslang.exe utils/mcp/main.das via popen_argv_pipe, drives initialize / tools/list / tools/call / method-not-found through JSON-RPC. Multi-chunk read loop for >16KB responses.
• tests/mcp/test_popen_argv_pipe.das — unit tests for the new builtin (echo round-trip, exit code propagation, stdin-EOF-after-block).
• tests/fio/popen_argv.das — new test confirming child stdin isolation (spawn echo fixture, no input → exits cleanly, no output).
• All new test dirs registered in tests/aot/CMakeLists.txt.

Docs

• daslib/logger added to das2rst.das with 5 groups (Setup / Level filters / Output control / Log calls / Stdout hook) + handmade module-logger.rst + sec_io.rst toctree entry.
• iso8601_now categorized under "Time and date"; popen_argv_pipe under "OS specific routines" in builtin/fio doc groups. Handmade descriptions for both.
• skills/daslib_modules.md updated with logger entry.

Test plan

• Interpreter test suite: 9079 tests, 9073 passed, 6 skipped
• AOT test suite: 8423 tests, 8417 passed, 6 skipped
• Lint: 0 issues across all 12 changed .das files
• Format: all changed .das files already-formatted
• Sphinx HTML build: build succeeded, no warnings
• MCP server smoke: starts, logs JSON Lines to logs/mcp_server.log, exits cleanly on stdin EOF
• JIT smoke (array.das, test_bulk_create.das): no verifier failures
• Pre-push hook (formatter --verify + lint changed files): passed

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR hardens MCP stdio behavior by adding structured logging, introducing bidirectional argv-based subprocess pipes, isolating child stdin, and migrating MCP launch/log paths away from inherited stdio.

Changes:

• Adds daslib/logger with JSON Lines logging and runtime stdout hook support.
• Adds/updates fio builtins for iso8601_now, popen_argv_pipe, and child stdin isolation.
• Adds MCP subprocess tests, logger tests, AOT registration, and related docs/metadata.

Reviewed changes

Copilot reviewed 21 out of 22 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
daslib/logger.das	New structured logger module and debug-agent hook.
daslib/command_line.das	Marks command_line as shared public.
src/builtin/module_builtin_fio.cpp	Adds timestamp and bidirectional subprocess pipe builtins; hardens popen_argv.
include/daScript/simulate/aot_builtin_time.h	Declares iso8601_now.
include/daScript/simulate/aot_builtin_fio.h	Declares popen_argv_pipe.
utils/mcp/main.das	Migrates MCP startup/shutdown logging to logger.
utils/mcp/protocol.das	Replaces bespoke MCP logging with logger wrappers.
utils/mcp/tools/live.das	Replaces system() launcher calls with captured argv subprocess calls.
tests/daslib/test_logger.das	Adds logger behavior tests.
tests/mcp/test_mcp_jsonrpc.das	Adds MCP JSON-RPC subprocess smoke tests.
tests/mcp/test_popen_argv_pipe.das	Adds unit tests for bidirectional pipe builtin.
tests/mcp/_fixture_echo.das	Adds echo fixture for subprocess pipe tests.
tests/mcp/_fixture_exit.das	Adds exit-code fixture for subprocess pipe tests.
tests/fio/popen_argv.das	Adds child stdin isolation regression test.
tests/aot/CMakeLists.txt	Registers logger and MCP tests for AOT.
doc/reflections/das2rst.das	Adds logger docs generation and builtin grouping updates.
doc/source/stdlib/sec_io.rst	Adds logger to I/O docs toctree.
doc/source/stdlib/handmade/module-logger.rst	Adds logger module documentation.
doc/source/stdlib/handmade/function-fio-popen_argv_pipe-0x2641eff84d0ce246.rst	Adds popen_argv_pipe docs.
doc/source/stdlib/handmade/function-builtin-iso8601_now-0xc27a33e76b6556df.rst	Adds iso8601_now docs.
skills/daslib_modules.md	Adds logger module skill entry.
.gitignore	Ignores generated logs directory.

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[Copilot]

Pull request overview

Copilot reviewed 21 out of 22 changed files in this pull request and generated 5 comments.