spawn io worker for drive subsystem (SYN-10499)

[invisig0th]

Overview

This branch introduces a dedicated IO worker subprocess for the Cell Drive subsystem.
The Drive's LMDB slab is migrated out of the shared Cell slab into its own file
(slabs/drive.lmdb) and is served from a separate process via Unix domain sockets
and the existing Telepath RPC framework. The change also modernizes dyndeps naming
conventions and improves subprocess coverage collection in CI.

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New Files

File	Purpose
synapse/lib/spawner.py	Generic IO worker spawner framework (SpawnerMixin, _ioWorkProc, _spawnerWait)
synapse/tests/test_lib_spawner.py	Tests for spawner timeout, OSError, and signal-handler paths
synapse/tests/test_lib_drive.py	Drive tests (moved out of test_lib_cell.py) plus backup-sync test
.coveragerc.main	Main-process coverage config (no multiprocessing tracer)
changes/c56856d0929e4a71fde0d98fc77ddeb5.yaml	Changelog: drive slab migration
changes/fb1de9c8091f353422a50736baf4d803.yaml	Changelog: dedicated IO worker for drive

Changed Files

File	Summary
synapse/lib/drive.py	New FileDrive subclass with SpawnerMixin; many sync methods converted to async; schema callback resolved via reqDynCoro; callback signature gains curv parameter
synapse/lib/cell.py	Drive init via FileDrive.spawner(); sockdirn for Unix sockets; _driveCellMigration copies drive DB to dedicated slab; drive.sync() called in backup and shutdown paths; drive API calls changed from sync to async
synapse/lib/dyndeps.py	New getDynCoro/reqDynCoro for async function import; tryDynMod/tryDynLocal/tryDynFunc deprecated in favor of reqDynMod/reqDynLocal/reqDynFunc; improved error messages
synapse/lib/link.py	New unixwait() polling helper for socket availability
synapse/lib/const.py	New UNIX_SOCKET_PATH_MAX = 103 constant
synapse/cortex.py	tryDynFunc -> reqDynFunc
synapse/datamodel.py	tryDynFunc -> reqDynFunc
synapse/tools/storm/pkg/gen.py	tryDynMod -> reqDynMod
synapse/tools/utils/autodoc.py	tryDynLocal -> reqDynLocal
synapse/tests/test_lib_cell.py	Drive tests removed (moved to test_lib_drive.py); socket path constant updated
synapse/tests/test_lib_base.py	Spawner fini lifecycle tests (Haha class)
synapse/tests/test_lib_dyndeps.py	Tests for getDynCoro/reqDynCoro/reqDynMod/reqDynLocal/reqDynFunc/runDynTask error paths
synapse/tests/test_lib_link.py	Test for unixwait()
synapse/tests/test_lib_agenda.py	Event loop mock moved inside getTestCore context
synapse/tests/test_lib_stormtypes.py	Event loop mock moved inside getTestCoreAndProxy context
synapse/tests/test_lib_nexus.py	Size threshold relaxed (3x -> 4x) to account for drive slab
.circleci/config.yml	COVERAGE_PROCESS_START added; --cov-config=.coveragerc.main for main process
.coveragerc	Subprocess coverage config: concurrency = multiprocessing, parallel = True, sigterm = True
scripts/testrunner.sh	Coverage flags updated; switched to --dist worksteal -n 8
docs/conf.py	SIGTERM warning pattern added to ignore list
CLAUDE.md	Coverage command example updated

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Architectural Detail

Spawner Framework (synapse/lib/spawner.py)

1. SpawnerMixin.spawner(base, sockpath) returns a factory coroutine.
2. The factory calls _spawn() which:
   • Serializes the __anit__ constructor call as a todo tuple.
   • Falls back to a /tmp/<guid> socket path if the configured path exceeds UNIX_SOCKET_PATH_MAX.
   • Launches a subprocess via s_process.spawn() running _ioWorkProc.
   • Waits for the socket with _spawnerWait (1-second poll, 30-second deadline).
   • Opens a Telepath proxy to unix://<sockpath>:item.
   • Registers bidirectional fini handlers (proxy fini -> subprocess fini -> base fini, and base fini -> proxy fini).
3. _ioWorkProc runs asyncio.run() in the subprocess, creates a Daemon, instantiates the target object, shares it, and listens on the Unix socket.

Drive Migration (cell.py + drive.py)

• Version 1 (_drivePermMigration): Migrates perm -> permissions field (existing).
• Version 2 (_driveCellMigration): Copies all drive rows from the shared cell slab into a new dedicated slab at slabs/drive.lmdb, then drops the old DB.
• After migration, FileDrive.spawner() initializes the drive in a subprocess.

Schema Callback Change

setTypeSchema callbacks are now specified as importable Python dotted-path strings (e.g., 'synapse.tests.test_lib_drive.migrate_v1') instead of raw function references. They are resolved at call time via reqDynCoro, which validates that the target is an async coroutine function. The callback signature also gains a fourth curv parameter (the current schema version before the upgrade).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.74%. Comparing base (6dc9f70) to head (a23c25c).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #4567    +/-   ##
========================================
  Coverage   97.74%   97.74%            
========================================
  Files         298      299     +1     
  Lines       62998    63142   +144     
========================================
+ Hits        61576    61719   +143     
- Misses       1422     1423     +1     

Flag	Coverage Δ
linux	97.67% <100.00%> (+<0.01%)	⬆️
linux_replay	93.47% <100.00%> (+0.01%)	⬆️

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