feat(miner-hands): shared subprocess redaction/env-allowlist helper in gittensory-engine

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Generalizes the CLI-subprocess driver's (#4266, this batch) reuse of redactSecrets and SUBSCRIPTION_CLI_ENV_ALLOWLIST/subscriptionCliEnv into a proper, engine-hosted, reusable helper — rather than every future subprocess-spawning driver (or anything else in gittensory-miner) copy-pasting the pattern from src/selfhost/ai.ts by hand. Today that pattern lives entirely in src/selfhost/ai.ts (SUBSCRIPTION_CLI_ENV_ALLOWLIST at line 349, subscriptionCliEnv at line 391, redactSecrets at line 724, resolveSubscriptionCliPath at line 375) — none of it is exported from packages/gittensory-engine, so #4266's driver either duplicates it or (better, and what this issue is for) the shared bits get promoted to the engine package where both src/selfhost/ai.ts and the new driver can depend on the same source of truth.

Deliverables

• packages/gittensory-engine/src/miner/subprocess-env.ts (or equivalent path) exporting a generalized env-allowlist builder (parameterized allowlist, not hardcoded to SUBSCRIPTION_CLI_ENV_ALLOWLIST's exact list — a coding-agent subprocess may need a different/larger allowlist than a review-only CLI call) and a generalized secret-redaction function lifted from redactSecrets's pattern (src/selfhost/ai.ts:724-731) — carry over the SECRET_PATTERNS regex family too (src/selfhost/ai.ts:339-346), not just the function shape.
• Decide and document the migration story for src/selfhost/ai.ts's existing copy: refactor it to import from gittensory-engine (matching the shim pattern src/rules/predicted-gate.ts already uses over packages/gittensory-engine/src/predicted-gate.ts), or leave it a parallel copy for now with a comment cross-referencing the new shared helper. Either is acceptable, but must be a deliberate, documented choice — an un-shimmed duplicate is exactly the kind of drift risk issue 🧩 Wave 2 — Analyze, Plan, Create & Deploy (HELD tracker) #2353's Phase 7 section flags as having already bitten signals/change-guardrail.ts once.
• Reuse (import, not copy) this helper from feat(miner-hands): CLI-subprocess CodingAgentDriver (reuse SpawnFn/redactSecrets/EFFORT_TIMEOUT_MS pattern) #4266's CLI-subprocess driver once both land — if feat(miner-hands): CLI-subprocess CodingAgentDriver (reuse SpawnFn/redactSecrets/EFFORT_TIMEOUT_MS pattern) #4266 lands first with its own inline copy, this issue's scope includes refactoring feat(miner-hands): CLI-subprocess CodingAgentDriver (reuse SpawnFn/redactSecrets/EFFORT_TIMEOUT_MS pattern) #4266 onto the shared helper instead of leaving two copies.
• Tests for the parameterized allowlist (confirm a caller-supplied allowlist is honored, not just the hardcoded default) and the carried-over SECRET_PATTERNS regex family (OpenAI/Anthropic keys, GitHub tokens, JWTs, AWS keys — same coverage redactSecrets already has, ported not weakened).

References

• src/selfhost/ai.ts:339-404 (SUBSCRIPTION_CLI_ENV_ALLOWLIST, resolveSubscriptionCliPath, subscriptionCliEnv)
• src/selfhost/ai.ts:339-346 (SECRET_PATTERNS)
• src/selfhost/ai.ts:724-731 (redactSecrets)
• Issue 🧩 Wave 2 — Analyze, Plan, Create & Deploy (HELD tracker) #2353's Phase 7 tracker note on src/rules/predicted-gate.ts → packages/gittensory-engine/src/predicted-gate.ts as the existing shim-over-engine pattern to mirror if choosing to refactor src/selfhost/ai.ts onto this shared helper
• Depends on / cross-references feat(miner-hands): CLI-subprocess CodingAgentDriver (reuse SpawnFn/redactSecrets/EFFORT_TIMEOUT_MS pattern) #4266 (this batch) — the concrete driver this helper's pattern is extracted from

[linear-code]

JSO-3271