fix(wasm-helpers): unique sandbox exec capture id per entity (ARN-401)

[rita-aga]

What

The sandbox exec output-capture temp files /tmp/.paw-{out,err,rc}-<id> collided between concurrent execs on one sandbox. unique_run_id() used only a process-local AtomicU32 starting at 0 — but every trigger dispatch is a fresh WASM instance, so the counter reset to 0 each time and every exec reused /tmp/.paw-out-00000000. Two concurrent execs then crossed each other's stdout and raced the cleanup delete.

Live impact (ARN-401): a governed ReleaseRun rollback ran concurrently with a healthy release's health probe on the same computer; the rollback's sandbox_exec returned the probe's 502 __HTTP_STATUS body instead of the git revert output, so a successful revert was reported as Failed.

Fix

Scope the capture id to the calling entity: capture_run_id(ctx.entity_id, host_clock, per-instance seq). Two different entities' execs never collide (different entity_id); the clock + counter separate repeats from one entity/instance. The entity id is sanitized to a filename-safe token (can't escape /tmp/.paw-* or break the shell redirect); empty falls back to exec.

Tests

capture_run_id unit tests: entity-scoped (the two-concurrent-entities case), repeat separation, and shell/path sanitization. 3/3 pass.

Deploy note

wasm-helpers is a shared path dep; the exec path is computer_exec (paw-compute). This PR fixes the source on main; computer_exec is rebuilt against it and republished to Genesis separately. Pairs with ARN-397 (per-repo release serialization) which prevents the overlap at the workflow level.

Linear: ARN-401

🤖 Generated with Claude Code

https://claude.ai/code/session_01PZkYwk1gmU6GPKRuQsSLda

Greptile Summary

The PR scopes sandbox-exec capture filenames using the calling entity, host time, and a per-instance sequence to prevent concurrent executions from sharing output files.

• Adds filename-safe entity-ID sanitization and an empty-ID fallback.
• Updates the Tensorlake execution path to use the contextual capture ID.
• Adds unit coverage for entity scoping, repeated execution, and unsafe characters.

Confidence Score: 4/5

The PR appears safe to merge, with a non-blocking uniqueness gap for distinct entity IDs that sanitize to the same filename token.

The new entity, clock, and sequence tuple addresses the reported common collision, but replacing every unsafe character with _ means distinct punctuated entity IDs can still converge on the same capture paths under simultaneous dispatch.

Files Needing Attention: os-apps/paw-agent/wasm/wasm-helpers/src/sandbox.rs

Important Files Changed

Filename	Overview
os-apps/paw-agent/wasm/wasm-helpers/src/sandbox.rs	Adds entity-scoped capture IDs and tests, but the lossy sanitizer does not strictly preserve uniqueness between distinct IDs.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    A[Entity ID] --> B[Replace unsafe characters with underscore]
    B --> C[Append host milliseconds and instance sequence]
    C --> D[Build out, err, and rc paths]
    D --> E[Execute and capture command output]
    A1[Distinct ID a/b] --> B
    A2[Distinct ID a?b] --> B
    B --> F[Possible identical sanitized token]
    F --> C

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Prompt To Fix All With AI

### Issue 1
os-apps/paw-agent/wasm/wasm-helpers/src/sandbox.rs:738-744
**Lossy entity-ID sanitization**

If distinct entity IDs such as `a/b` and `a?b` execute concurrently on the same sandbox during the same clock millisecond, this mapping gives both the same sanitized token and capture paths, allowing their output to cross or one invocation to delete the other's files.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "fix(wasm-helpers): make sandbox exec cap..." | Re-trigger Greptile}

Greptile also left 1 inline comment on this PR.

[greptile-apps]

Lossy entity-ID sanitization

If distinct entity IDs such as a/b and a?b execute concurrently on the same sandbox during the same clock millisecond, this mapping gives both the same sanitized token and capture paths, allowing their output to cross or one invocation to delete the other's files.

Prompt To Fix With AI

This is a comment left during a code review.
Path: os-apps/paw-agent/wasm/wasm-helpers/src/sandbox.rs
Line: 738-744

Comment:
**Lossy entity-ID sanitization**

If distinct entity IDs such as `a/b` and `a?b` execute concurrently on the same sandbox during the same clock millisecond, this mapping gives both the same sanitized token and capture paths, allowing their output to cross or one invocation to delete the other's files.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.