pi-extensions/docs/adr/0001-recover-full-bash-command-from-session.md

status

status
accepted

Recover the full Bash command from the Pi session

Mechanism superseded by ADR 0004. Permission-system 25.3 now exposes the complete local Bash input through PromptPermissionDetails.payload; the wrapper and complete-compound safety rules recorded here remain in force.

pi-permission-inner-cmd needs the complete Bash input before it may allow a transparent wrapper. @gotgenes/pi-permission-system exposes only the winning command unit as details.command; for timeout 60s pnpm test && git push, that may be timeout 60s pnpm test. An Authorizer allow approves the whole tool call, so unwrapping that unit alone could hide a sibling command.

Decision

For direct calls to Pi's native bash tool, capture the session manager at session_start. During authorization, walk the session in reverse to the latest assistant message containing a toolCall block whose id equals details.toolCallId, require exactly one such block within that message, and read its structured arguments.command value.

Proceed only when all evidence agrees:

• the request and recovered tool call both identify the native bash tool;
• the tool-call ID has exactly one match within the latest assistant message that contains it (a cross-message reuse resolves to the latest, which is the call being authorized);
• arguments.command is a string;
• the ask-triggering unit (details.command) matches the wrapper grammar;
• the inner command is not another recognized wrapper.

V0.1 recognizes:

^timeout[ \t]+([1-9][0-9]*(?:\.[0-9]+)?[smhd]?)[ \t]+(.+)$

The duration follows GNU timeout's grammar: a positive number (integer or decimal) with an optional unit s/m/h/d (default seconds), so a bare integer such as timeout 240 cmd is accepted. The duration format is irrelevant to unwrap soundness — the duration is discarded and only the inner command is re-evaluated — so the full numeric grammar is allowed. 0/leading-zero, ms, and flags remain excluded. (Amended from the original unit-required grammar after timeout 240 … was seen in real usage.)

The complete inner command is re-evaluated through the Deterministic Permission Policy. Map allow to allow, deny to deny, and ask to defer. Missing or ambiguous session evidence, forwarded requests, shell aliases, unsupported timeout options, nested wrappers, parse failures, and exceptions all produce defer.

Scaffolded commands (amended). The recovered full command may be a compound that does not start with the wrapper — e.g. a subagent scaffold cd … && timeout … | tail; echo EXIT. Detection therefore runs on details.command (the unit the permission system isolated, always wrapper-leading). The wrapper is stripped from the full command (the unit text is replaced by its unwrapped inner, required to occur exactly once) and the entire de-wrapped compound is re-evaluated through the Deterministic Permission Policy, which decomposes it into units and keeps the most restrictive — so sibling commands are still judged and cannot hide behind the wrapper's allow. If the unit is not a recognized wrapper, cannot be located exactly once, or the re-evaluation is not allow, the authorizer defers fail-closed. (The original design detected on the full command only, which missed every scaffolded command; details.command is now used for detection and locating only — judgment still runs on the full command, preserving the "never trust a truncated unit" rule.)

Consequences

This avoids changing permission-system and avoids parsing authorization evidence from the human-facing details.message. It deliberately supports fewer contexts: forwarded and non-native shell calls continue through the existing authority chain.

The implementation must retain regression tests for:

• inner allow, ask, and deny mapping;
• compound input such as timeout 60s pnpm test && git push;
• unsupported and nested wrapper syntax;
• missing, within-message duplicate, malformed, and forwarded session evidence;
• a tool-call id reused across messages (resolved to the latest);
• Authorizer registration and disposal.

The end-to-end experiment confirmed that permission-system checks every Bash command unit but invokes the Authorizer once for the aggregated ask; an Authorizer allow then releases the complete tool call. See context ownership and minimal Bash judgment evidence for the underlying permission and evidence boundaries.

Rejected alternatives

• Treat details.command as the full input: unsafe for compound Bash programs.
• Parse details.message: fail-closed parsing is possible but couples authorization to UI prose.
• Add a permission-system API: structurally clean, but would make this package depend on an unavailable upstream change.
• Maintain a safe-command allowlist: duplicates policy and violates the re-evaluation invariant.