Use BEFORE dispatching implementer/reviewer subagents (superpowers:subagent-driven-development) or BEFORE extending a layer in this repo. Catalog of concrete past failure modes specific to this project — subagent dispatch checklists + sibling-code grep obligations + spec problem-statement enforcement.
Installation
Installer avec Codex ou Claude Copiez ce prompt, collez-le dans Codex, Claude ou un autre assistant, puis laissez-le vérifier la page du skill et l'installer pour vous.
Use BEFORE dispatching implementer/reviewer subagents (superpowers:subagent-driven-development) or BEFORE extending a layer in this repo. Catalog of concrete past failure modes specific to this project — subagent dispatch checklists + sibling-code grep obligations + spec problem-statement enforcement.
Concrete past misses on this project. Each entry has:
What went wrong — the specific incident with commit refs
Why it slipped review — the mechanism that let it through
Mitigation — what to insert into implementer / reviewer prompts to catch it next time
These are NOT generic best practices — they are this-project trap-pattern documentation derived from incidents on main. Read this BEFORE you start dispatching subagents or writing a fresh implementation. They are the most cost-effective additions to your subagent prompts.
What went wrong: The Phase B spec (docs/superpowers/specs/2026-05-22-server-mode-runner-reverse-dial-design.md) said in the Problem section that ALL harness-cli subcommands on a runner host suffer from ACL outbound block. But the Implementation section was titled "Phase B: Agent leg = objproto negotiated proxy" — and the implementation shipped covering only the agent subcommand. User caught it months later: harness-cli ls from inside a runner-spawned process silently failed because cli.Dial didn't check the proxy env.
Fixed in commit 2365260 (moved proxy detection into cli.DialPeerConn, shared by every subcommand).
Why it slipped review: The reviewer subagent compared the diff to the Implementation section only. Spec compliance was technically PASS. The Problem section was never re-read during review.
Mitigation — insert into IMPLEMENTER prompts:
Step 0: read the spec's Problem statement verbatim (not the Implementation section alone). In your final report, enumerate the problem-statement bullets and state which ones the diff addresses. If any bullet is left unaddressed, justify the omission explicitly.
Mitigation — insert into REVIEWER prompts:
Read BOTH the spec's Problem statement AND the Implementation section. Flag any problem-statement bullet not covered by the diff. "Spec compliance" review against only the Implementation section misses scope contractions that happen in the spec itself.
Pitfall 2 — Invented labels harden into unwritten constraints
What went wrong: The Phase B spec used the label "Agent leg" (which I invented, undefined). The label semantically narrowed the scope from "all harness-cli on runner host" to "agent subcommand", but the narrowing was never written down — the label just felt narrower than the actual problem. User: "agent leg という言葉がそもそも定義がよくわからない".
Same incident as Pitfall 1, same fix (2365260).
Why it slipped review: A vague label feels rigorous. Reviewers and implementers treat it as authoritative without checking what it actually denotes.
Mitigation — when writing specs:
Describe the concrete mechanism in plain terms, NOT a label
If a label is unavoidable, state IN/OUT scope explicitly immediately after introducing it
Beware labels like "X leg", "Y side", "Z axis", "design intent", "state precondition" — these are tells
Tells of the same pattern (feedback_jargon_masks_confusion in memory): if you find yourself constructing terminology to describe what code SHOULD do, you probably don't fully understand the mechanism yet. Read the code first.
What went wrong: When adding the --via flag for server dial-runner across CLI/TUI/WebUI, the implementer copied the high-level cli.ServerDialRunner(ctx, server, target, via) pattern (which does Dial + defer Close — appropriate for the short-lived harness-cli binary) into TUI and WebUI. But TUI and WebUI already hold a long-lived *cli.Client from snapshot polling; they should have used cli.ServerDialRunnerWith(ctx, c, ...) instead. Every server dial-runner from TUI/WebUI was opening a fresh WS conn + ECDH + PSK + Hello, throwing away the existing client.
Fixed in c55ed45 (TUI/WebUI use the *With variant on a.client / currentClient()).
Why it slipped review: Implementer's view was confined to the cli helper. The reviewer compared against the spec which said "extend cli.ServerDialRunner" — also literally satisfied. Neither asked "how does DoSubmit / DoCancel call into cli? Should this new caller follow the same pattern?".
Mitigation — insert into IMPLEMENTER prompts when adding code to TUI/WebUI/server handlers:
Step 0: grep how sibling code in this layer calls into the same helper category. Specifically for TUI: every existing Do* function (DoSubmit, DoCancel, DoInteractive, DoSessionList, ...) threads a.client through. Your new DoX MUST follow the same pattern, NOT the harness-cli binary's Dial+Close pattern.
Mitigation — insert into REVIEWER prompts:
Does this diff use the same helper-invocation pattern as adjacent code in the same layer? Spec compliance alone is not enough — check layer-internal consistency.
Pitfall 4 — Build-output / runtime-state collision in make clean
What went wrong: make clean was rm -rf bin. bin/.run/ is the runtime state directory for scripts/runner.sh (slot pid / log / shutdown sentinel files). Live agent-runner processes kept their --shutdown-file path open across the delete; subsequent restart attempts via scripts/build_and_restart_all.py reported "no alive agent-runner slots under bin/.run/" because the orchestrator could no longer discover them.
Fixed in commit fe62101 — make clean now removes only the four specific binary targets, preserving bin/.run/.
Why it slipped: bin/.run/ was added to the project after make clean was written. No one re-audited the clean target.
Mitigation — when adding state under an existing build-output directory:
Audit make clean / git clean / build scripts for the new path. Better: don't co-locate runtime state with build output (this project should eventually move bin/.run/ to .run/ at repo root, but kept as-is to avoid a coordinated restart of all live runners).
What went wrong: runner/relay_handler.go's completeRelaySetup initially called pc.Close() after SetProxy. peer.Conn.Close() sends a trsf.Close wire message before tearing down — but that wire Close reached the SERVER's end-to-end relay conn (which shares the same CID through SetProxy) and caused handleConnection on the server to exit EOF prematurely, before the target runner's RunnerHello arrived.
Fixed in commit 101128d — use pc.Connection().Close() (raw objproto-level close, no trsf Close message). The proxySettings entry survives, the activeConn entry is removed, packets keep being forwarded.
Why it slipped: Discovered only by the E2E integration test (TestRelayE2E). Unit tests didn't catch it.
Mitigation — when working with peer.Conn and objproto.Connection:
peer.Conn.Close() ≠ pc.Connection().Close(). The former sends a trsf.Close wire message (semantically "I'm leaving"); the latter tears down only the local activeConn state. For SetProxy-style relay setups, you almost always want the latter — sending wire Close would propagate through the proxy to peers you didn't mean to notify.
peer.Conn.Close() also has a load-bearing 50ms sleep for Windows scheduling (project_peer_close_send_drain in memory) — that's the other half of the same close-behavior surface.
Pitfall 6 — Listen bind addr ≠ dial target addr
What went wrong: HARNESS_PROXY_VIA_RUNNER was set to literal cfg.WSListen (e.g. "ws:0.0.0.0:8540-*"). Agents on the same host tried to dial 0.0.0.0:8540 — accepted by Linux kernel as localhost, rejected by Windows / macOS. With --listen :8540 (host empty) the agent got ws::8540-* which fails DNS lookup on every OS.
Fixed in commit d26aa8d — rewriteProxyViaForLocalDial normalizes the host portion to loopback when it's an unspecified bind address.
Why it slipped: Tested only on Linux. The cross-OS issue was theoretical until somebody actually ran it on Windows / macOS — at which point it's a confusing late failure.
Mitigation — when generating addr strings for cross-host / cross-OS use:
Distinguish bind addr (server-side, "listen on every interface" = 0.0.0.0) from dial addr (client-side, "where to reach this peer" = 127.0.0.1 / hostname / specific IP). Never use the bind addr as a dial target. If you're auto-deriving one from the other, write a rewrite step explicitly.
Pitfall 7 — Specs that punt decisions to "implementer's choice"
What went wrong: While writing the chained-relay spec, I left four design points unresolved with phrases like "implementer's choice", "or kept as dead code temporarily", "could be deferred to a separate change if scope creeps", "Implementer must decide between (a) ... (b) ... (c) ...". User caught it: "implementer decision的なところが残るのは何でなん?".
Fixed in commit 3c99b39 — each punt converted to an explicit decision in the spec body. Open questions section renamed to "Decisions taken".
Why it slipped: When the spec author is unsure between two paths, deferring "to the implementer" feels collaborative. It isn't. The implementer doesn't know which to pick either, will either freeze on it or default to the easiest path without recording rationale (cf. Pitfall 1, scope contraction). A "could be deferred" line in a spec means: the spec is incomplete and pretending to be complete.
Mitigation — when writing specs:
If you find yourself writing any of these phrases, STOP and decide before committing:
"implementer's choice"
"could be deferred to a separate change"
"remove or deprecate" (pick one)
"or kept as dead code temporarily"
"Implementer must decide between (a)... (b)... (c)..."
"TBD", "TODO" inside the spec body (open questions section is fine, but they should be USER decisions, not implementer's)
For each, ask: "What would I do if I were implementing this right now?" Write that as the decision. If the spec genuinely needs the user's input on a tradeoff, mark it as an explicit open question for the USER, not the implementer.
Difference from a legitimate open question:
Legitimate open question = user must make a tradeoff call (e.g. "do we want SSO support in v1 or v2?"). Spec waits for user.
Implementer-punted decision = author doesn't want to pick (e.g. "remove or keep as dead code"). Both options are author-decidable; user shouldn't have to.
Pitfall 8 — Harness worktree silently diverges from parent's branch
What went wrong (2026-05-24): All 21 commits of chained-relay spec / plan / code work landed on the parent repo's feature/chained-relay-spec branch, while the harness task worktree's actual branch (harness/<hash>) stayed at its old HEAD. User caught it when ls .claude/skills from the worktree showed only harness-cli (missing implementation-pitfalls), while ls from the parent repo showed both. By then the worktree's branch was 148 commits behind the work the controller "thought" it had done. Controller had also incorrectly claimed "the 2 worktree-unique commits are already on origin/main" based on commit-message matching alone — content diff showed they were different code.
Root mechanism:
Harness spawns the task with cwd = /home/.../remote-agent-harness/.harness-worktrees/<hash>/ on branch harness/<hash>.
Edit / Write tools called with absolute paths under /home/.../remote-agent-harness/<rel> resolve to the PARENT repo's main checkout — not the worktree (feedback_worktree_path_routing).
git -C /home/.../remote-agent-harness <op> similarly operates on the parent's .git and the parent's currently-checked-out branch.
Result: controller does Edit ... && git add ... && git commit ... from the worktree session, but everything actually lands on the parent. Worktree stays frozen. Controller's git log (which also routes to parent) reports the new commits, so the divergence is invisible until someone ls from the worktree side.
Mitigation — when controlling a harness task on this repo:
Decide upfront where work lands, and stick to it for the entire task:
Parent repo (default): explicitly tell every subagent to operate in /home/kforfk/workspace/remote-agent-harness/ and verify branch. See "Subagent dispatch checklist" below.
Fresh non-harness worktree: user creates a worktree outside .harness-worktrees/ (e.g. /home/kforfk/workspace/remote-agent-harness-impl/) and you operate there. Avoids routing entirely.
The harness worktree itself: only OK for read-only work (verifying state, running tests). Do NOT commit from inside — commits route to parent unpredictably.
Verify before claiming "commits are on the right branch":
git -C <path> log --oneline -5 to confirm
git worktree list to map directories ↔ branches
Never assume two same-name commits across branches are the same content — git diff <sha1> <sha2> or git cherry is the only way to know.
When the user asks "is the branch up to date with origin/main?", run git fetch && git log origin/main..HEAD && git log HEAD..origin/main AND git worktree list AND git -C <worktree> rev-parse --abbrev-ref HEAD. The single-source-of-truth answer is the worktree HEAD's actual branch's relationship to origin/main, NOT the parent repo's checkout state.
What went wrong (2026-07-03): Resume-conversation and runner-selection work was repeatedly checked through only one operator surface at a time. The CLI had explicit --resume-conversation flags in submit, interactive, and session new; the TUI task-list keybindings had equivalent behavior via r/u versus R/U; WebUI task-sheet actions later gained assigned-runner and any-runner resume variants. But the separate command-entry surfaces were not checked at the same time:
TUI has a bottom command line (tui/cmdline.go) distinct from its task-list keybindings. It parses --resume for submit, interactive, and session new, but does not parse --resume-conversation.
WebUI has a command input (webui/static/main.jsrunCmd) distinct from its task-sheet buttons. Its submit command uses the Resume task id field but does not set resumeConversation.
So "TUI supports resume conversation" was true for task-list keys but false for the TUI command-line route. "WebUI supports resume conversation" was true for task-sheet buttons and resumeTaskById, but false for the WebUI command input. These are different user-visible entry points and must not be collapsed into one mental bucket.
Why it slipped review: The controller asked "does TUI have it?" and answered from the most visible TUI path. It did not enumerate every operator entry point. The same happened for WebUI: task-sheet buttons were treated as the whole WebUI, while the command input was a separate parser with different request construction.
Mitigation — before implementing or reviewing any operator-visible flag/option:
Build an explicit surface matrix and fill every cell before claiming coverage:
Surface
Check
CLI binary
cmd/harness-cli/main.go, cmd/harness-cli/session.go, help text, CLI tests
If a feature intentionally omits a surface, document the omission in the diff or spec. "No parser there" is not an implicit excuse; the absence itself is a design decision.
Mitigation — insert into IMPLEMENTER prompts for operator-facing features:
Before editing, enumerate CLI, TUI keybindings, TUI cmdline, TUI popups, WebUI buttons/forms, WebUI cmdline, WASM bridge, shared cli/server/runner handling. For each, say "implemented", "not applicable", or "intentionally omitted because ...". Do not report "TUI/WebUI done" unless both their direct controls and command-entry surfaces were checked.
Mitigation — insert into REVIEWER prompts:
Audit operator-surface parity. For every new flag/option/request bit, verify CLI, TUI keybindings, TUI cmdline, WebUI buttons/forms, WebUI cmdline, and WASM bridge separately. Flag any surface where the parser accepts a related option like --resume but drops the companion option like --resume-conversation.
Pitfall 10 — A .bgn wire change wipes the runner fleet (server-first, and prove the skew is recoverable)
What went wrong (2026-07-16): landing appended fields on RunnerHello
(agent_profiles) while the server — which runs on a DIFFERENT host — still ran
the old binary. The old server could not decode the new hello, found no identity
union, and answered PskAuthStatus.no_identity. That was classified FATAL, so
PersistLoop exited instead of retrying: all 12 runner slots died within ~1s
and none returned when the server was upgraded. Each needed manual recovery
(flags recovered from bin/.run/agent-runner-<tag>.restart.log).
The asymmetry that makes this easy to trip: make build + /restart-all on the
runner host upgrades ONLY the runners. The server is a separate host and stays
old unless you restart it too — restart the SERVER first.
Fixed in d4f7a5a + follow-up: no_identity is now RETRYABLE
(cli.PskRejectedError.Retryable) — BadPsk/BadTicket stay fatal (credential
failures no retry can fix), a version skew now costs a reconnect, not a wipe.
That only helps once BOTH ends carry it, so the restart order still matters.
Why it slipped: the fatal/retryable line was drawn at "explicit rejection vs
transport drop", and no_identity was swept into the fatal set on an unexamined
assumption — cli/psk.go literally said "should not happen: we always embed a
hello". True for our own bugs; false for a version-skewed server that cannot
DECODE a hello we DID send.
Mitigation — before landing any .bgn change:
scripts/wire-skew-check.sh # OLD_REF defaults to merge-base with origin/main
It builds both sides, runs NEW runner × OLD server, and asserts the failure is
RECOVERABLE (rejected → retries → self-heals when the server is upgraded). It is
a no-op (exit 0) when no .bgn changed, so it is safe to run unconditionally.
Note what it deliberately does NOT assert: that skew works. This project has no
compat shims by design; asserting "works" would push us toward shims we do not
want.
Two sub-lessons, both learned the hard way while building that check:
A guard that cannot fail is worse than none. The check's first version
passed on everything: a fresh git worktree add has no
webui/static/main.wasm (gitignored build artifact) and harness-server
refuses to start without it, so the runner only ever saw "connection refused"
and "it retried" was trivially true. It now proves the skew was exercised
(a real rejection reached the runner) before it may report PASS — and a
non-starting old server is a setup error (exit 2), never a pass. Always run
the negative control: make the fix absent and confirm the check goes red.
Don't hand-build the same struct at N sites — give it a constructor.PskRejectedError was built raw at three sites; the fix added a Code field
and a grep scoped to cli/ missed the third — the runner has its OWN
handshake (sendRunnerMergedHandshake in runner/connect.go, because it
sends a RunnerHello not a ClientHello). The zero Code read as
PskAuthStatus_Ok, Retryable() returned false, and the fatal behaviour was
silently restored. Unit tests could not catch it: they hand-built the struct
too, so they never exercised a creation site. Now there is one field and one
cli.NewPskRejectedError(status). When adding a field to a struct built in
several places, add a constructor (or delete the derived field) rather than
trusting a grep — and grep the whole repo, not the package you expect.
See also Pitfall 3 and feedback_enumerate_all_callsites_when_intercepting.
Subagent dispatch checklist (controller-side)
When dispatching an implementer or reviewer subagent in this project, include in the prompt:
Hard preconditions (every subagent prompt — non-optional)
Parent repo, not harness worktree: Work in /home/kforfk/workspace/remote-agent-harness/, NOT in any .harness-worktrees/<hash>/ directory. Verify branch with git rev-parse --abbrev-ref HEAD before writing code. Use absolute paths under the parent repo for all tool calls. Past incident: 148 commits diverged silently because writes via absolute path routed to parent while the worktree HEAD stayed on an unrelated harness/<hash> branch.
Read this file first: Read .claude/skills/implementation-pitfalls/SKILL.md in full before writing code. The catalog is short; each entry was triggered by a prior incident. Subagents that skip it tend to recreate the same failure mode.
Implementer prompt augmentations
Quote the spec's Problem statement verbatim. Report which bullets the diff addresses; justify omissions.
Sibling-code grep: before adding code to TUI/WebUI/server handlers, grep how adjacent files in the same layer invoke the same helper category. Match the existing pattern.
Operator-surface matrix: for operator-visible flags/options, check CLI, TUI keybindings, TUI cmdline, TUI popups, WebUI buttons/forms, WebUI cmdline, WASM bridge, and shared cli/server/runner handling separately. Do not collapse "TUI" or "WebUI" into a single surface.
Beware peer.Conn.Close() vs pc.Connection().Close() when working with relays.
Build hygiene — keep the worktree clean. Compile-check with go build ./... (builds everything, writes NO binary) or go build -o /dev/null ./cmd/<x> / go vet ./cmd/<x>. NEVER bare go build ./cmd/<x>/ — that drops a <x> executable into the worktree root. go test ./... cleans up after itself; don't go test -c without -o /dev/null. Stray harness-tui / *.test binaries pollute git status, get caught by git add -A, and leave junk in the user's worktree. The cwd must be exactly as clean after your checks as before.
Reviewer prompt augmentations
Read BOTH the Problem statement AND the Implementation section. Flag uncovered problem-statement bullets.
Check layer-internal consistency: does this diff's caller pattern match adjacent code in the same layer?
Check operator-surface parity: CLI, TUI keybindings, TUI cmdline, TUI popups, WebUI buttons/forms, WebUI cmdline, WASM bridge, and shared cli/server/runner code must either all support the feature or have explicit documented omissions.
Check for silent fallback paths: if a config / env is set, does any combination cause it to be ignored without log?
Spec-writing checklist (controller-side, before commiting a spec)
Grep the draft for "implementer's choice", "could be deferred", "remove or", "TBD", "TODO". Decide each before committing.
Grep for "Wait —", "hmm", "let me think" — these are author-uncertainty markers that don't belong in a spec body. Verify the underlying logic and rewrite confidently or mark as an explicit open question.
Problem statement and Implementation section must cover the same scope. If the Implementation section silently narrows scope, the rationale must be written in the spec body (not just left as a label change).
When to invoke this skill
BEFORE running superpowers:subagent-driven-development for any task on this project
BEFORE dispatching a fresh implementer or reviewer subagent
BEFORE writing new code that touches: cli.Dial*, peer.Conn.Close, transport.WebSocketEndpoint mode handling, env injection for spawned processes, HARNESS_PROXY_VIA_RUNNER, make clean, or any helper that has *With(client) long-lived and X(serverCID) short-lived variants
Project principles (from user-level memory)
These are user-driven feedback rules from past sessions, baked into project-local form so subagents on this repo see them. Each one was triggered by a specific past incident; the one-liner is enough to remember the rule, expand by reading the named memory file if needed.
Scope / sizing
Individual dogfood scope (feedback_individual_dogfood): No external users. Don't inflate breaking-change / migration concerns. Renames, subcommand splits, schema field additions are quality fixes — just do them. Don't add migration shims, deprecation periods, or backward-compat layers "for users" that don't exist.
Don't split schema/spec across plan tasks (feedback_no_split_schemas): When a plan adds new wire types or config fields, put the FULL schema/interface in ONE plan task. No "also add this in Task N" follow-ups — the schema becomes harder to review and easier to diverge against. Same for spec docs: keep the authoritative byte layout in one place.
Protocol / schema discipline
Schema describes every byte on the wire (feedback_no_schema_invisible_bytes): The .bgn files are the single source of truth. Any byte sent on the wire MUST be described in the schema. "Convention puts this byte here" is worse than "schema doesn't mention it" — schema becomes a lie.
Protocol explicit over convention (feedback_protocol_explicit_over_convention): If a field is needed, extend the schema. Don't write code that "by convention puts X in this position of the payload". LLMs lose convention context across sessions; explicit schema fields survive.
Reading before writing
Read harness code before architectural speculation (feedback_read_code_before_arch_speculation): Don't reason from 1-line memory summaries or vague impressions. When proposing a structural change, first check README + relevant main.go + handler implementation. Memories can drift; code is authoritative.
Jargon masks confusion (feedback_jargon_masks_confusion): When unsure of how a layer behaves, the next step is reading the schema / handler. Not constructing "design intent" / "state precondition" / "[X]-axis" prose. Treat invented framing words as tells that you don't fully understand yet. (See also Pitfall 2 above for the spec-writing variant.)
Verification discipline
Verify fix in symptom env BEFORE writing memory (feedback_verify_before_memory_writes): Hypotheses codified as memory mislead future sessions when wrong. Push the code fix freely, but hold the explanatory memory until you've actually seen the original symptom go away with your change applied. This catalog file is bound by the same rule.
Harness / runtime
Harness worktree paths route to parent repo (feedback_worktree_path_routing): Inside a harness task, /home/.../remote-agent-harness/<rel> resolves to the parent's main checkout, not the per-task worktree. Anchor edits explicitly to the worktree when needed; bash commands cd <abs path> land on the parent.
Spawn runners via scripts/runner.sh up --as TAG (feedback_use_runner_scripts): Never hand-roll nohup setsid bin/agent-runner .... The script handles slot allocation, pid/log files, detach, restart. Bypassing it leaks state under bin/.run/.
Bundle related repos via --roots (feedback_runner_roots_bundle): "Add repo B to runner A" = extend A's --roots, not a new --as slot per repo. One runner can serve multiple roots.
harness-cli never sync wait/dispatch from agent turn (feedback_no_sync_wait_dispatch): send only and end the turn. Replies arrive via inbox hook on a later turn. Applies to the initial harness.hello handshake too. Synchronous wait stalls the entire conversation.
Naming / labels
Invented labels in specs become implicit constraints (feedback_invented_terms_become_implicit_constraints — see also Pitfall 1 & 2): Vague labels in specs (e.g. "Agent leg", "X-axis", "design intent") feel rigorous but harden into narrow implementations. Describe the mechanism in plain terms. If a label is unavoidable, state IN/OUT scope explicitly right after introducing it.
Layer consistency
Reuse long-lived *cli.Client in TUI/WebUI (feedback_reuse_long_lived_client — see also Pitfall 3): When adding a new helper, expose both X(serverCID) (short-lived: dial+close) and XWith(client) (reuse). TUI/WebUI MUST call the *With variant against their existing a.client / currentClient() — never the high-level fresh-dial form.
Check existing patterns before extending a layer (feedback_check_existing_patterns_before_extend — see also Pitfall 3): Before adding a new TUI / WebUI / server-handler entry, grep how sibling code in the same layer invokes the same helper category. Subagents copy what they see first (often a test pattern or CLI pattern) which is usually wrong for production. Controller must show them the forest.
Sources
Project-local incidents (Pitfalls section) — commit refs on main
User-level memory (~/.claude/projects/.../memory/feedback_*.md) — accumulated across sessions, mirrored above
