fix(agent): recover or flag pending attachments that fail to reach the cloud agent

[fercgomes]

Problem

Closes GROW-99

Pasting a prompt into PostHog Code auto-converts it to a pasted-text.txt attachment. On cloud tasks the file is uploaded as a run artifact and the sandbox agent reads it from .posthog/attachments/…. Intermittently the agent instead received the bare task description Attached files: pasted-text.txt as plain text — no file, no inline content — and replied that it "can't find the file… no text was included inline", unable to do the task. (The task title also stayed Untitled.)

Root cause

In agent-server.ts → sendInitialTaskMessage, when getPendingUserPrompt() returns null (no pending message and no resolvable artifacts) it falls back to task.description. For a pasted-text-only task that description is just the Attached files: … summary, so the agent is handed a prompt naming a file it was never given. The artifact fails to resolve when the run's artifacts manifest doesn't yet contain the just-uploaded pending_user_artifact_ids — most likely a transient manifest lag at run start.

Fix

Hardened getPendingUserPrompt:

1. Best-effort recovery — refetch the run manifest once when a declared attachment isn't listed yet, so a transient lag doesn't drop the attachment (the pasted text then reaches the agent).
2. Safe degraded prompt — if an attachment still can't be hydrated, append an explicit "the attachment didn't come through, ask the user to paste it directly or re-send" notice instead of the misleading bare description. Skill bundles (installed silently) are excluded from the count.
3. Adds a warn("Pending user attachments could not be loaded", …) log with resolved/expected counts, so a consistent failure (artifact genuinely missing server-side) is obvious in run logs.

The misleading task.description fallback in sendInitialTaskMessage is now bypassed for this case, and the resume paths benefit too since they share getPendingUserPrompt.

Tests

New AgentServer pending user attachments suite in agent-server.test.ts:

• missing attachment (refetch also empty) → explicit notice appended, not null
• refetch recovers the artifact → resource_link block, no notice
• no pending artifacts → null, and no refetch

Typecheck and Biome are clean.

The file's existing HTTP-mode tests run a git commit in createTestRepo, which is blocked in the signed-commits sandbox this was authored in — so I couldn't run them locally. The new tests are deliberately self-contained (no git/HTTP) and pass; CI covers the rest.

Notes

• This was seen as a one-off, so the change hardens the degraded path and adds recovery rather than chasing a root cause I couldn't confirm. If it reproduces every time, the new warn log points at the artifact genuinely not landing in taskRun.artifacts server-side.
• The earlier title fix (fix(sessions): name tasks from pasted text-file contents #2850) is unrelated — it only touched name generation, not how the file reaches the agent.

Closes GROW-99

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit e44adde.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(agent): recover or flag pending atta..." | Re-trigger Greptile}

[greptile-apps]

_{Reviews (2): Last reviewed commit: "fix(agent): avoid duplicate "missing art..." | Re-trigger Greptile}