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# Harness, SDK & wire protocol — guide (generic tier)

Reference notes, design rationale, and negative results (14).

#### 1. Trust source code over docs and pin constants to the live system, validated programmatically
`generic` · _see related: U0439 (other tier)_

When you have the server or source, treat code as ground truth and docs as drift-prone. Pin operational constants to the artifact the runtime actually loads (a live manifest/config the system reads), not a plan or prose: a plan and the authoritative config routinely disagree, and a config that interleaves schema defaults with per-variant overrides gives the wrong value if you audit only one block. AST-parse the cited source files for the constants and overwrite extracted or prose values, failing the doc on disagreement, because prose archaeology fabricates values and invents nonexistent fields (one pass produced 5 of 6 wrong payloads and invented spurious actions). Verify packet sizes, bit masks, endpoints, and auth fields against the actual running server, and validate the pinned values with a typed/parser check (AST or a Pydantic-style schema) so a stale constant fails loudly rather than silently shipping.
  <sub>sources: auggie:5d1ff8d5-2505-4dca-af45-56d3070363e2, claude-code:067e7439-cbd1-4b26-9b3f-d054bde3aa40, claude-code:33356b24-de19-46ae-ad01-810557f4d9b1, claude-code:f70c9801-7ee7-499b-97f9-4fd0848a6b8e (+5)</sub>

#### 2. Treat live schema and engine source as authority over the local checkout; map drift structurally
`generic` · ⚠ _session-derived, unverified_

Treat the running system and its live schema as authority over a local checkout, because checkouts drift; use the checkout to understand the algorithm but pull the live schema/contract before building calls against it, and when a typed client crashes fall back to the raw API (e.g. a server wrapping rows in a paged envelope the local client expected as a bare list; routes present in source yet absent from the published schema dump). Distinguish 'empirically true' from 'mechanistically true' and verify against the implementation, not client docs: a claim documented in many places can be wrong at the mechanism level (e.g. 'slot 0 is always role X' was true only because the default seed happened to shuffle that way; the real mechanism was a seeded Fisher-Yates). When a pinned/vendored dependency breaks an import, do NOT blindly rename to the 'did you mean X?' symbol; that often hides a structural split (one monolithic config split into a connection object and a separate runtime/env config, typically extra='forbid'). Trace the new module structure and map every old field before editing; minimize blast radius by returning the narrowest object callers use; a new keyword-only param with a default is backward-compatible. Build first to baseline upstream drift before adding a feature, and when a build error sits in code you didn't touch, confirm it predates your change (check a sibling) before assuming you broke it.
  <sub>sources: codex:019ea93a-43b0-7800-b34e-7b3053c46177, codex:019ea9af-7020-7550-b427-d3478fed2057, opencode:ses_20be14977ffeIxGxctKKzW9s1y, opencode:ses_201bc0c24ffe4uYJuw52Gs42LG (+2)</sub>

#### 3. Audit an LLM behavior menu across four axes and find the deterministic shadow policy that really decides
`generic` · **negative result** · ⚠ _session-derived, unverified_

When auditing the menu of behaviors/tools exposed to an LLM, check four distinct axes per behavior: nominal (the registry/parser knows the name), advertised (it appears in the system prompt), really available (a runtime path can activate it and it passes the guard), and does-something (its handler emits real effects, not a no-op). A behavior can pass the first three and still be a pure no-op; an advertised no-op is worse than an absent one because the LLM picks it and wastes turns. The legality/availability guard and the prompt description are independent sources of truth that silently diverge (one capability was legal in code far more broadly than the prompt claimed). Even when telemetry shows the LLM as the decision source most of the time, real authority can live in default selection and reflex/fallback paths, so locate every strategic choice the LLM did NOT actually make before claiming it controls the agent.
  <sub>sources: codex:019e196e-93c2-7523-8da7-96f782ea578c</sub>

#### 4. Select the LLM provider explicitly from env; a missing key is not 'LLM disabled'; copy a working sibling's config
`generic` · **negative result** · ⚠ _session-derived, unverified_

Make LLM provider selection explicit and env-driven with a fixed first-match precedence so the same code runs local and hosted: disable-flag => deterministic-only; a platform credential flag (e.g. USE_BEDROCK / CLAUDE_CODE_USE_BEDROCK=1) truthy => the platform client with platform creds; a first-party key set => first-party API for local testing; else => scripted/deterministic only. NEGATIVE: a provider hardcoded to one API treated a missing first-party key as 'LLM off' and silently ran with no LLM in an environment that actually had platform (Bedrock) credentials -- a missing key is NOT 'LLM disabled'. An enable flag being set does not mean a call happens (provider availability is a separate gate); verify the high-value path actually executed by looking for guidance/strategy traces, not merely that the process ran without erroring. Boolean-ish flags are easy to misread (DISABLE=0 means do-NOT-disable; only 1/true/yes/on count; a baked-in default-on image env can re-enable a feature on the wrong provider): verify against the parser, audit every place the feature can be enabled, never assume 0 means off. When adding an LLM brain on a shared platform account, copy the model id, region, and client config from a known-working sibling rather than guessing (e.g. a proven config: AnthropicBedrock, a us.* cross-region inference-profile model id, the right region, temperature 0, capped max_tokens, tight timeout). For high-volume workloads default to the cheapest capable model behind an env override, because cost/latency dominate.
  <sub>sources: codex:019e14a5-e574-7770-953b-17019f2f5e74, codex:019e184d-2de6-7b22-b8c0-853edbf53265, codex:019e2886-d576-7770-be1b-6d92ca97761e, codex:019ea93a-43b0-7800-b34e-7b3053c46177 (+2)</sub>

#### 5. Verify the LLM path works inside the deployed container; confirm the backend from runtime logs, not config
`generic` · **negative result** · ⚠ _session-derived, unverified_

An LLM integration that works locally can silently no-op in a hosted environment because credential resolution differs by host -- e.g. a resolver that knows only local env keys and one cloud role mechanism yields no_key when the host schedules the workload under a different mechanism (web-identity token file / role-ARN). Missing hosted creds are a SILENT degrader (the system falls back to weaker behavior, not a crash). Confirm the ACTIVE backend from runtime logs, not intended config: a bare model id in logs (vs an inference-profile id) means the intended backend was never selected even with a 'use backend X' commit, because the enable flag never reached the workload; a direct-API 404 'model use case not submitted' means the account is gated, not a code bug, and tuning prompts changes nothing -- fix access or run without the flag. Read the exact exception type/message to localize the backend (a direct first-party API 404 is NOT a platform-backend failure and proves the direct path was used). To isolate an env-injection bug to the right layer, check whether the per-job secret bundle actually contains the flag (it did, yet the workload still used the wrong path, proving the break was downstream of bundle creation). Mitigation: resolve credentials for the mechanism the host actually uses and emit a startup init trace recording the selected provider and present auth env vars, so a no_key failure self-diagnoses from logs.
  <sub>sources: auggie:ac491a46-e7f7-4271-a1c0-f0e69987d424, claude-code:307f1069-21fb-469e-bcd2-8a07f2dba0d8, claude-code:3837ef5e-3e9c-41bc-b290-df5865581698, claude-code:3bdbae7f-58b2-4e0e-880b-2a2e03cc0aad (+4)</sub>

#### 6. Honor the dispatcher submit() contract on the synchronous path; suspect result-plumbing when the LLM connects but emits nothing
`generic` · **negative result** · ⚠ _session-derived, unverified_

When a dispatch interface has both async-polling and synchronous paths, honor the submit() return contract on BOTH. A dispatcher built around async polling left the sync HTTP path half-wired: submit() computed a valid completion, stored it in a local, discarded it, and returned false, which the caller read as an error. A synchronous result needs a place to live (a syncResult/syncReady slot the poll step checks) or it is silently lost. When an LLM provider connects at startup but no output appears, suspect the dispatch/result-plumbing layer, not auth or the API call: verify the result is delivered to the consumer, not merely that the call was made. If a confirmation that LLM/reflex layers are even active is needed, check the logs (all decisions carrying directive_source:'default' means pure scripted play, dormant reactive/LLM layers).
  <sub>sources: opencode:ses_20422c08ffferRLvWnNE5DeB4w, opencode:ses_21a0d30b6ffewSKOVSUyO4lZkU</sub>

#### 7. Nim/ORC: never share GC state across threads; channels never delivered in the bot binary -- use subprocess polling or a Unix-socket JSON protocol
`generic` · **negative result**

In threaded native programs (e.g. Nim under --mm:orc), global mutable state (cached secrets, connection pools, history buffers) is a GC-safety and data-race hazard the moment a worker thread touches it, and a {.gcsafe.} pragma alone does NOT fix it. NEGATIVE: Nim Channel.tryRecv under ORC never delivered messages inside the real binary despite a passing standalone test, across every variant tried (create()-allocated channels, module-level globals, {.threadvar.} globals -- which wrongly make per-thread copies so the worker writes a different variable than main reads -- and atomic-flag-gated blocking recv() which blocks forever) -- a passing standalone tryRecv test does not prove it works in the real binary. Working alternatives: own runtime state PER INSTANCE behind a stable heap pointer (module-global worker threads/channels caused cross-instance leakage and a shutdown hang where close() joined a shared worker; do not pass a pointer into a resizable array to a worker thread); make worker state thread-local or pass it through channels; create fresh per-call resources (new HTTP pool per request); have the worker serialize events to plain JSON strings pushed over a channel and drained on main; or use subprocess polling (spawn, poll process.running() each frame). For a native-core-plus-out-of-process-helper design, define an explicit typed message protocol over a Unix-domain socket using newline-delimited JSON with a small set of message types. Transport NEGATIVE: avoid shelling out to curl/python per call (higher latency); prefer in-process or a local socket/pipe with a fast native path and a non-blocking slow path. Pass an explicit timeout into outbound HTTP calls, map timeouts distinctly from other HTTP errors, and keep shutdown idempotent.
  <sub>sources: opencode:ses_21a8f9dedffekGKNrfPfGruC81, opencode:ses_21b008642ffeCM6Q48G44aM6k0, opencode:ses_21b02c437ffeor4lV5Nb4Cec7y, opencode:ses_21b1e7074ffeYT9RjQFHNPlNKX (+3)</sub>

#### 8. Native FFI worker: init explicitly from a native-owned thread, never lazily on the hot path; audit teardown across the FFI boundary
`generic` · **negative result**

Spawning a native worker thread lazily from inside a per-frame FFI call running on a foreign (Python ctypes) thread races on shared channels/state and produces memory corruption (deadlock, SIGSEGV, or caught-exception noop depending on timing). Start any background worker once via an explicit init entrypoint from a thread the native side controls, never lazily from the hot per-frame path on caller-owned threads. Whether an FFI-loaded library auto-initializes its runtime on load is checkable, not guessable: inspect the compiled dylib for a constructor / mod_init_func section rather than assuming a build flag like --app:lib guarantees one. Lifecycle/teardown that writes analysis artifacts can be silently severed across an FFI boundary: trace manifests stayed 'closed:false' with missing end_tick/outcome/role because there was no destroy_policy export on the native side and no close()/__del__ on the Python wrapper to call it, so closeTrace/writeManifest(final=true) never ran -- when episode artifacts are incomplete, audit the whole teardown call chain end to end, not just the writer. A crash that only surfaces during shutdown can hide the real per-frame failure: a SIGSEGV appeared in teardown (destroyBot during policy.close()) but in the real match SIGTERM killed the process before close() ran, so only the silent noop showed; when a bug reproduces in your harness but not production (or vice versa), check whether teardown order differs. Distinguish 'gameplay broke' from 'shutdown broke': with a fake API key gameplay still moved (~45% non-noop) but the process never exited because policy.close() joined a worker blocked in an in-flight HTTP call.
  <sub>sources: opencode:ses_201637e3bffeRa6Y0x3DOs8hh1, opencode:ses_20b1744aeffettq8pxHNVgjKNC, codex:019dfea2-76a2-7ba0-996a-9be68ceee04f</sub>

#### 9. A catch-all except that returns a stale default turns every crash into silent inaction; strip or log it before theorizing
`generic` · **negative result** · ⚠ _session-derived, unverified_ · _see related: U0508 (other tier)_

When a system produces no observable output ('does nothing' / outputs only the inert default), trace the full pipeline end to end before fixing anything: apparent inaction usually stacks several independent layers, not one bug. A catch-all `except Exception` around a per-iteration decision that returns a stale default (a no-op) on any failure turns every crash into SILENT inaction with no error surfaced -- strip or log that handler first so the real exception shows, rather than theorizing about the downstream logic. Distinguish 'strategically correct but inert' (the high-level mode/decision is right yet the unit emits nothing actionable) from 'wrong decision', and diagnose the selection layer and the action-emission layer separately, since correct transitions say nothing about whether the chosen path emits real work.
  <sub>sources: opencode:ses_1fa65507bffexDcakAPT4pHA1d, opencode:ses_201637e3bffeRa6Y0x3DOs8hh1, opencode:ses_21ab38af3ffeCyRfclXzAswGm1, opencode:ses_1f7b6dc30ffeDmQtlUZI25HAjh (+3)</sub>

#### 10. Two parallel lookup tables silently drift; derive both from one source and never fall back to a silent default on an unmapped value
`generic` · **negative result** · ⚠ _session-derived, unverified_ · _see related: U0509 (other tier)_

Two parallel index->value lookup tables maintained independently silently drift out of sync (one case: a native table grouped one way and a parallel reimplementation grouped another disagreed on 22 of 27 entries) and garble behavior with no loud failure. Derive both from ONE canonical source, or add a build-time assertion that fails if their orderings diverge. A 'fall back to index 0 / a default' on an unrecognized key is a silent-corruption trap that looks like a deliberate choice; prefer raising or logging on an unmapped value so corruption surfaces. Where an enum's integer values back persisted records or index static dispatch tables, treat it as schema-stable: appending is safe, but reordering or deleting a mid-list entry shifts every later value and silently corrupts old records -- leave a dead stub rather than reorder, and re-export shared enums rather than duplicating them (duplicates drift and cause subtle equality bugs).
  <sub>sources: opencode:ses_21ab38af3ffeCyRfclXzAswGm1, opencode:ses_21eb30b06ffeL6353Ov27zhdA1, opencode:ses_1fed7bbaaffe4qARc9KvRdpGAC, opencode:ses_2067f7b41ffe0wSvJ4MZlE58Q1</sub>

#### 11. Identical lockstep behavior across independent actors signals a determinism bug; give each randomness consumer its own RNG substream
`generic` · **negative result** · ⚠ _session-derived, unverified_ · _see related: U0510 (other tier)_

When multiple supposedly-independent actors behave identically in lockstep (e.g. all drift the same way at once), suspect shared deterministic logic firing in sync -- a determinism bug -- before blaming the domain logic: check whether the decision source is actually deterministic and whether the actors share a start condition (a stub that always returns the same output produces exactly this). Give each randomness consumer its OWN RNG substream rather than one shared global RNG, since a shared RNG lets any reordering of calls silently change behavior and defeats reproducibility/parity testing. Add a cheap divisibility/size invariant to fixed-width binary dumps (a corrupted capture is caught when total bytes stop dividing evenly by the fixed record size).
  <sub>sources: opencode:ses_20c066070ffeBjXMnfQULai0Lw, opencode:ses_20a41d230fferPYcSsh385tuSR, opencode:ses_224322057ffexj7SYlcfVA0zgy</sub>

#### 12. Run a multi-language agent fleet as per-agent subprocesses with a uniform CLI, auto-discovered by folder convention
`generic` · tool: `run_agents.py` · _see related: U0523 (other tier)_

For a multi-language or multi-process agent fleet, standardize on a per-agent runnable SCRIPT invoked with a uniform CLI (e.g. --url and --name), NOT an importable in-process class: agents in any language are then wrappable, one crashing cannot kill the others, and each is debuggable standalone. (Subprocess-per-instance only loses to in-process for sub-millisecond coordination or shared GPU, which most fleets do not need.) Auto-discover agents by folder convention (an agent exists iff <dir>/<name>/<entry>.py exists), using the directory name as id; gate main() behind `if __name__=='__main__'` so importing for metadata is side-effect-free; generate per-instance names from a single global counter (baseline_1, baseline_2, ...); and have the supervisor forward SIGINT/SIGTERM to all child subprocesses, warning and continuing if one crashes rather than exiting on the first death.
  <sub>sources: opencode:ses_21b899dadffeBiSiDW3XWFqEdz, opencode:ses_21e7dd4d4ffewtISu38YXrsOgs, opencode:ses_224322057ffexj7SYlcfVA0zgy, opencode:ses_20c066070ffeBjXMnfQULai0Lw (+2)</sub>

#### 13. Player binaries are working-dir sensitive; audit fixed-depth parent-climb path helpers when restructuring layout
`generic` · ⚠ _session-derived, unverified_

A binary that loads resources (config, fonts, maps, palettes) at startup is sensitive to its working directory. When such a process crashes silently while a coordinator reports it as merely 'not ready', read the process's own stderr/log FIRST, because the cause is often a missing-asset/path error during init, not a networking failure. Two processes can reach resource loading through different code paths, so 'it works for process A' does not prove process B's path logic -- validate each binary's path resolution independently. Any path helper that climbs a FIXED number of parent dirs (e.g. parentDir().parentDir()) is a latent bug the moment a file's nesting depth changes (moving foo into foo/foo breaks a two-level climb); audit such helpers whenever restructuring layout. An init line like setCurrentDir(baseDir()) can be a harmless no-op or a meaningful directory change depending on which definition of the helper is in scope, so resolve which one compiles in before assuming the line is boilerplate.
  <sub>sources: opencode:ses_200deb284ffe7RFSHqkkWQqwAx</sub>

#### 14. Define a derived feature once over an abstract event stream and parity-test all adapters that feed it
`generic` · _see related: U0528 (other tier)_

When the same derived feature must be computed from two different data sources (e.g. an offline/batch source and a live/streaming source), define each feature ONCE over an abstract event-stream interface and feed it via thin adapters (one per concrete source), then add parity tests asserting all adapters produce identical features on the same input. This guarantees a model fitted on the offline data behaves identically when driven live, and prevents the two code paths from silently diverging.
  <sub>sources: personal_labs/crewrift_lab/crewrift/crewborg/docs/designs/suspicion-le, personal_labs/crewrift_lab/crewrift/crewborg/docs/trace-logs.md, personal_labs/crewrift_lab/AGENTS.md, personal_labs/crewrift_lab/README.md (+2)</sub>
