Summary

gstack-config set brain_trust_policy@local personal fails with a validation error when gbrain is configured as a stdio (local PGLite) engine, making /setup-gbrain report DONE_WITH_CONCERNS and silently skip writing the trust policy.

Root cause

endpoint_hash() in bin/gstack-config intentionally falls back to the literal string "local" when no MCP URL is found (stdio engines have no URL to hash):

# bin/gstack-config ~L161
# MCP server URL. Falls back to the literal 'local' when no MCP is configured.
endpoint_hash() {
  ...
  printf '%s' "local"   # ← stdio fallback
}

The comment at L138 even documents this intent:

#   brain_trust_policy@<hash>  — unset on fresh install; setup-gbrain
#                                writes 'personal' for local engines,

However, the key validator on both get and set only allows hex characters after @:

# get (L265) and set (L280) — same pattern in both
if ! printf '%s' "$KEY" | grep -qE '^[a-zA-Z0-9_]+(@[a-f0-9]+)?$'; then
  echo "Error: key must contain only alphanumeric characters, underscores, and an optional @<hex-hash> suffix" >&2
  exit 1
fi

local contains l and o which are outside [a-f0-9], so the key brain_trust_policy@local is rejected even though endpoint_hash() produces it by design.

The same hex-only pattern also appears in the get value-lookup grep (L270).

Affected lines

Fix

Change [a-f0-9]+ → [a-zA-Z0-9]+ at all three sites. This covers both sha8/sha16 hex hashes (remote endpoints) and the local fallback (stdio engines) without opening up anything unsafe.

# get + set validators
grep -qE '^[a-zA-Z0-9_]+(@[a-zA-Z0-9]+)?$'

# get value lookup
grep -E "^${KEY%@*}(@[a-zA-Z0-9]+)?:"

Error message wording should also drop "hex-" from "optional @<hex-hash> suffix".

Observed behaviour

/setup-gbrain on a stdio/local-PGLite engine reports:

DONE_WITH_CONCERNS — minor:
gstack-config set brain_trust_policy@local personal fails validation because
the @<hash> suffix regex requires hex-only ([a-f0-9]+) and endpoint-hash
returns the literal 'local' for stdio engines.

The trust policy is never written; the concern is non-fatal but visible on every /setup-gbrain run.

Verified in

~/.claude/skills/gstack commits a5833c4 (v1.57.10.0) and 8241949 (v1.57.9.0) — present in both.