Runtime HAL for multi-runtime agent orchestration. Detects active AI assistant (Claude Code, Codex, Gemini, Cursor) and exposes uniform interface for startup injection, GUPP enforcement, and communication selection.
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Runtime HAL for multi-runtime agent orchestration. Detects active AI assistant (Claude Code, Codex, Gemini, Cursor) and exposes uniform interface for startup injection, GUPP enforcement, and communication selection.
type
skill
category
orchestration
status
stable
origin
tibsfox
modified
false
first_seen
2026-03-06T00:00:00.000Z
first_path
.claude/skills/runtime-hal/SKILL.md
superseded_by
null
Runtime HAL
Hardware Abstraction Layer for AI coding assistant runtimes. The HAL detects which runtime environment is active and provides a uniform interface so that every other skill in the Gastown chipset can operate identically regardless of runtime. This mirrors Gastown's internal/runtime/runtime.go provider abstraction, where the Go binary auto-detects its host environment and adapts its hook, nudge, and session strategies accordingly.
In the chipset hardware metaphor, the Runtime HAL is the BIOS/UEFI firmware layer. Real firmware probes hardware on boot, detects what peripherals exist, and presents a uniform interface to the operating system. The HAL does the same: it probes the runtime on activation, detects what capabilities exist (hooks, session IDs, context forking), and presents a uniform interface to the chipset's skills and agents.
Activation Triggers
This skill activates when the task involves:
Determining which AI coding assistant runtime is active
Selecting a startup injection strategy for an agent
Choosing a GUPP enforcement mechanism (hooks vs polling vs preamble)
Configuring stall detection thresholds or nudge intervals
Adapting behavior based on runtime capabilities (hooks, context fork, session ID)
Debugging why an agent is not receiving hooks or nudges
HAL Interface
The HAL exposes a uniform interface that other skills consume. No skill outside the HAL should inspect environment variables, probe the filesystem for runtime indicators, or check the process tree directly.
These types are also declared in the shared Gastown type system at src/chipset/gastown/types.ts. The HAL consumes AgentRole from the same module when generating startup commands.
Provider Detection
Detection runs once at activation time and caches the result. The detection cascade follows Gastown's runtime.go pattern, which tries the most specific signal first and falls through to progressively weaker indicators.
Detection Cascade
Step 1: Explicit override via GT_RUNTIME environment variable
If GT_RUNTIME is set, use its value directly. This allows operators to force a specific provider during testing, CI, or when running inside a container where other signals are absent.
Step 3: Check for .claude/settings.json in workspace
If the workspace root contains .claude/settings.json, this strongly indicates a Claude Code environment. This catches cases where the session ID variable is not yet propagated (e.g., hook execution before session fully initializes).
Step 4: Check process tree for known runtime binaries
Inspect the process tree for known executable names:
Binary
Provider
claude
claude
codex
codex
gemini
gemini
cursor
cursor
This step is the least reliable (binary names can change across versions) and serves as a last-resort heuristic before falling back.
Step 5: Fall back to 'unknown'
If no signal matches, the provider is 'unknown'. The HAL selects the polling strategy for both startup and GUPP. This ensures graceful degradation: no crash, no hang, no error. The chipset operates in a reduced-capability mode where hooks are unavailable but work items still flow through periodic filesystem polling.
Detection Summary
GT_RUNTIME set?
yes -> use GT_RUNTIME value
no -> CLAUDE_SESSION_ID set?
yes -> 'claude'
no -> .claude/settings.json exists?
yes -> 'claude'
no -> process tree matches known binary?
yes -> matched provider
no -> 'unknown'
Provider Capabilities Matrix
Capability
Claude Code
Codex
Gemini
Cursor
Unknown
Session hooks
Yes
No
No
Partial
No
Context fork
Yes
No
No
Yes
No
Session ID env var
CLAUDE_SESSION_ID
GT_SESSION_ID
GT_SESSION_ID
None
None
Startup injection
SessionStart hook
gt prime fallback
gt prime fallback
Command palette
Polling
GUPP strategy
hook_injection
startup_fallback
polling
prompt_preamble
polling
Stall threshold
120s
180s
300s
120s
300s
Nudge interval
30s
60s
120s
30s
120s
Nudge support
Yes (filesystem)
Yes (filesystem)
Yes (filesystem)
Limited
Yes (filesystem)
Startup Strategies
The HAL selects a startup strategy based on the detected provider. Startup strategy determines how an agent receives its initial context (role, work item, GUPP rules) when it is spawned.
hook_injection (Claude Code)
Claude Code supports .claude/settings.json hooks that fire on session events. The mayor writes a SessionStart hook entry that injects the agent's role, assigned bead, and GUPP rules into the session context before the agent's first prompt. This is the highest-fidelity strategy: the agent starts with full context and never needs to poll for its assignment.
Codex does not support hooks. Instead, the mayor writes the agent's assignment to a known filesystem path, then starts the agent with a gt prime command that reads the assignment file on startup. The agent receives its context through command-line injection rather than hook callbacks.
Mayor writes assignment file -> gt prime starts agent -> Agent reads file -> Context loaded
polling (Gemini, Unknown)
For runtimes without hooks or startup injection, the agent starts with a generic context and immediately enters a polling loop, checking state/hooks/{agentId}.json at the configured nudge interval until it finds an assignment. This is the slowest strategy but requires zero runtime-specific integration.
GUPP (Guided Unsupervised Parallel Processing) enforcement varies by runtime capability. The HAL selects the most reliable GUPP mechanism available.
hook_injection (Claude Code)
GUPP rules are injected via hooks into the agent's session context. The agent operates under GUPP constraints enforced by the runtime itself. Stall detection works through hook callbacks: if the agent's lastActivity timestamp in the hook state exceeds the stall threshold, the witness raises an alert.
startup_fallback (Codex)
GUPP rules are baked into the agent's startup context via the gt prime command. The agent cannot modify its own GUPP constraints after startup. Stall detection relies on filesystem observation: the witness watches for changes in state/hooks/{agentId}.json and triggers if the file's modification time exceeds the threshold.
prompt_preamble (Cursor)
GUPP rules are prepended to the agent's prompt context via the command palette integration. This is less reliable than hook injection because the agent can potentially ignore preamble instructions. Stall detection works identically to the startup_fallback case.
polling (Gemini, Unknown)
GUPP rules are written to the hook state file. The agent polls for both work assignments and GUPP constraint updates. This is the most robust fallback: it requires no runtime-specific integration, but introduces latency equal to the nudge interval. Stall detection is inherent in the polling mechanism: if the agent stops polling (no reads on the hook file), it is stalled.
Error Handling
Unknown Provider Behavior
When the provider is 'unknown', the HAL guarantees:
No crash -- all interface methods return valid defaults
No hang -- polling uses bounded intervals, never blocks indefinitely
No error thrown -- detectProvider() always returns a valid RuntimeProvider
Operational -- work items still flow; agents still execute; merges still happen
This is the fundamental contract: the chipset degrades gracefully, never catastrophically.
Detection Failure Recovery
If detection throws an exception (corrupted settings file, permission denied on process tree), the HAL catches the error, logs a warning, and returns 'unknown'. No detection failure propagates to calling skills.
Session ID Absence
If getSessionId() returns null, the calling skill must not assume hooks are unavailable. Some runtimes set the session ID asynchronously. The HAL uses the full detection cascade (not just session ID) to determine capabilities.
Integration with Other Gastown Skills
Skill
How It Uses the HAL
mayor-coordinator
Calls getStartupStrategy() and getStartupCommands() when spawning polecats
polecat-worker
Calls getGUPPStrategy() to know how GUPP rules are enforced
witness-observer
Calls getStallThreshold() and getNudgeInterval() for monitoring timers
nudge-sync
Calls supportsNudge() to decide whether to send filesystem nudges
hook-persistence
Calls supportsHooks() to decide whether to write hook state files
beads-state
Uses getSessionId() to tag work items with the active session
No skill outside the HAL should perform its own runtime detection. If a skill needs to know the runtime, it calls detectProvider(). If it needs to know whether hooks work, it calls supportsHooks(). The HAL is the single source of truth for runtime capabilities.
Boundary: What the HAL Does NOT Do
The HAL NEVER:
Executes work -- it detects the runtime and exposes capabilities; it does not perform orchestration
Writes hook state files -- that is the responsibility of hook-persistence and beads-state
Sends messages -- that is the responsibility of mail-async and nudge-sync
Monitors agents -- that is the responsibility of witness-observer
Makes dispatch decisions -- that is the responsibility of mayor-coordinator
The HAL is a detection and capability layer. It answers "what can this runtime do?" but never "what should we do?"
Configuration Override
Operators can override HAL defaults via environment variables:
Variable
Purpose
Example
GT_RUNTIME
Force a specific provider
GT_RUNTIME=codex
GT_STALL_THRESHOLD
Override stall detection (seconds)
GT_STALL_THRESHOLD=240
GT_NUDGE_INTERVAL
Override nudge interval (seconds)
GT_NUDGE_INTERVAL=45
GT_GUPP_STRATEGY
Force a GUPP strategy
GT_GUPP_STRATEGY=polling
Overrides take precedence over provider defaults but not over structural impossibilities (e.g., forcing hook_injection on Codex will not make hooks appear).
References
references/gastown-origin.md -- How this skill maps to Gastown's internal/runtime/runtime.go
providers/claude-code.md -- Claude Code provider details and hook integration
providers/codex.md -- Codex provider details and startup fallback
providers/fallback.md -- Generic fallback provider for unknown runtimes
