refactor(mothership): sim-side quality pass + dead-code sweep from the parity hill-climb

Quality (25 verified findings from the review pass): the embedded CLI's
soft-fail exit code rode the process-global exitCode two parallel
invocations raced on — it now rides the EmbedContext (setSoftExitCode
seam, global fallback for the standalone CLI). Model-authored wire params
lose their bare as-casts for typeof guards (run segments, run-tool params,
output-file declarations, function-execute refs via one refField helper);
the six copy-pasted cancel-settlement blocks in the tool executor fold
into one settleCancelled; five error-completion literals into one builder;
three title-casing humanizers into one; the sandbox image cache moves from
a hand-rolled TTL map to lru-cache; sleepWithAbort yields to
interruptibleSleep; plus dead re-exports, a pass-through wrapper, a dead
param, an unreachable busy-spin branch made an invariant, and misc rule
violations (inline sleep/getErrorMessage/truncate, mid-file import,
retired-tool literal).

Dead code (verified-unreferenced, from the Go-era audit): four delegated
use-cases replaced by sim_cli, the file-subagent doc raster pipeline, env
secret-ref resolution, workflow-state prompt formatting, the runtime
stream-schema mirror (sync script trimmed to match), the workflow
checkpoint/revert feature (routes + contracts; table drop deferred), and
five orphaned copilot routes (update-messages, models, credentials,
rename, and the duplicate chat mount — /api/mothership/chat is the live
path). LONG_RUNNING_TOOL_IDS trimmed to the live tool surface with tests
re-anchored. Go-decommission-gated routes (tools/execute, key/byok
validate, inbandOwned) and policy items (steering chain, Go-era replay
titles) deliberately kept — listed in the audit doc for Sid.

Claude-Session: https://claude.ai/code/session_01CgaxNAaeD3taGdghbXn17w

Author: Sg312