Master's transactional loader made the invalid-provider PTY case regress:
the HMR main watcher's initial scan refreshed the include mid-initial-apply,
the concurrent group updates stranded the include fiber, and once serialized
the failing apply's rollback deadlocked on HMR's refresh drain — dsh exited
13 with no diagnostic and the terminal stranded, the exact symptom this
branch fixes. Serialize every include child-tree mutation through one queue
and pass ignoreInitial to the HMR main watcher; the failing boot now settles
through boot()'s labelled rejection with the tree disposed and exit 1. The
PTY case asserts the settled diagnostic; the fail-loud release remains the
guard for rejections boot cannot see.
tsconfig.base.json adds noUncheckedIndexedAccess,
exactOptionalPropertyTypes, noImplicitOverride,
noFallthroughCasesInSwitch, noUnusedLocals, and noUnusedParameters on
top of strict. Vendored packages opt out of the new flags locally
(their tsconfigs are ours to regenerate; their source is not), keeping
upstream-sync friendliness.
Our code fixed accordingly: index accesses acknowledge undefined
(assembler flush cursors, lastTurnNumber); optional properties are
omitted instead of set-to-undefined (GenerateResult.usage,
ToolDefinition.strict, GenerateOptions.system/tools, error payloads
via an errorData helper); Session.onAppend is explicitly
`(…) => void | undefined`; tests and examples updated for unused
parameters and indexed access.