fix: address PR review comments — traceback, CORS parsing, byte sizes, DecisionTree collapse

[Copilot]

Five issues identified in code review of the comprehensive bug-fix PR.

Changes

• context.py — TraceContext.__aexit__ used traceback.format_exc(), which reads the currently active exception rather than the exc_type/exc_val/exc_tb args passed to it. When invoked manually (e.g. in trace_tool/trace_llm) with no active exception, this produced "NoneType: None". Now uses format_exception(exc_type, exc_val, exc_tb) with a format_exception_only fallback when exc_tb is None.

• api/main.py — CORS origin list now filters empty strings after split/strip, preventing phantom entries from trailing commas (e.g. "https://a.com,") in AGENT_DEBUGGER_CORS_ORIGINS.

• collector/server.py — Size validators used len(json.dumps(v)) (character count), undercounting multi-byte characters. Switched to len(json.dumps(v, ensure_ascii=False).encode('utf-8')) for accurate byte enforcement.

• DecisionTree.tsx — collapse state — d.data._collapsed was set on the ephemeral D3 hierarchy node, which is fully reconstructed from convertToD3Tree(tree) on every render, discarding all mutations. Collapse state is now persisted in a stable collapsedStateRef: Map<string, boolean> keyed by event id and applied during hierarchy construction.

• DecisionTree.tsx — collapsed indicator selector — .node[data-id="..."] selector never matched because node <g> elements lacked the attribute. Added .attr('data-id', (d) => d.data.id) to the node selection.

• client.ts — Removed unused TreeNode import that was causing tsc to exit non-zero.

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[Copilot]

Pull request overview

This PR applies a focused set of follow-up fixes to address prior review comments across the SDK, API, collector, and frontend tree visualization—primarily improving traceback capture, configuration parsing, byte-accurate size validation, and persistent UI collapse behavior.

Changes:

• Fixes TraceContext.__aexit__ to format the exception from the provided (exc_type, exc_val, exc_tb) instead of relying on the currently-active exception.
• Hardens CORS origin parsing to drop empty entries and updates collector validators to enforce payload size limits in UTF-8 bytes.
• Persists DecisionTree collapse state outside the ephemeral D3 hierarchy and adds missing data-id attributes used by the collapsed indicator selector; removes an unused TS import breaking tsc.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
frontend/src/components/DecisionTree.tsx	Persist collapse state across renders via ref-backed map and ensure node elements get data-id for selectors.
frontend/src/api/client.ts	Removes unused TreeNode type import to keep tsc clean.
collector/server.py	Switches size checks from character count to UTF-8 byte count for correct DoS-limit enforcement.
api/main.py	Filters out empty CORS origins after split/strip to avoid phantom entries from trailing commas.
agent_debugger_sdk/core/context.py	Formats traceback from the exception arguments passed to __aexit__, fixing “NoneType: None” when no active exception exists.

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