fix(agent-sessions): decode tool-error payloads the way the session page does - #1148

🟡 Confidence 3/5 · needs attention
The query-engine source diffs were read at the head rather than as diffs, so only their final state was verified; the three test files I read as diffs are consistent with it.
_{quality 90/100 · 1 warning · tests covered · risk medium · 1/1 new units observable}

The tool-error payload path now hands back the span's attribute map (cut, with the true sizes of the values cut) and decodes arguments/result in TypeScript through aiToolCallPayload, instead of projecting a fixed pair of attribute keys in SQL — so the modal and MCP tool read a tool span the way the session page does. The read stays org-scoped and bounded by the page's own extent, and the three test files were updated to the new row shape.

• aiToolErrorPayloadsQuery returns spanAttributes plus cutAttributeBytes instead of arguments/result
• aiToolErrorPayload decodes the payload with aiToolCallPayload and truncates it by codepoint
• The payload read is bound by the page's own first and last timestamps, not the caller's window

Still open from earlier reviews

• 🟠 Warning · F1 · aiToolErrorPayloadsQuery ships each sampled span's full uncapped payload map · packages/query-engine-integrations/src/ai/ai-tools.ts:973

_{7525624 · Updated on every push. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}