Add remove() method to ChatContext for flexible item removal

[3eid]

Summary
Adds a public remove() method to ChatContext for removing items by ID, by ChatItem instance, or a sequence of either. This avoids the need to access the private _items list directly.

Problem
ChatContext already provides helpers like get_by_id() and index_by_id(), but no public way exists to remove an item. Users currently must manipulate _items directly:

idx = ctx.index_by_id(item_id)
if idx is not None:
    ctx._items.pop(idx)

Accessing _items relies on internal implementation details and can break if the structure changes.

Fix
Adds a remove() method that:

• Accepts a single ChatItem, an item ID (str), or a sequence of either.
• Returns a list of removed items (empty if none were found).

This follows the suggestion from @tinalenguyen to allow more flexible usage and aligns with existing helpers like insert().

Usage Examples

# Remove by ID
ctx.remove(item_id)

# Remove by ChatItem instance
ctx.remove(item)

# Remove multiple at once
ctx.remove([item_id_1, item_2])

Testing
Added comprehensive unit tests covering:

• Single removal by ID or ChatItem
• Removal of sequences (IDs, instances, or mixed)
• Partial matches and nonexistent IDs
• Removal from empty context
• Special cases like AgentConfigUpdate items

Closes #5085

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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[theomonnom]

Hey, this is great, but can we have a similar API to list.remove? Like https://docs.python.org/3/tutorial/datastructures.html#more-on-lists

[3eid]

Hey, this is great, but can we have a similar API to list.remove? Like https://docs.python.org/3/tutorial/datastructures.html#more-on-lists

Good idea.

To stay close to list.remove, I’ll make remove() operate on a single item and raise if not found.

For the input, I’m leaning toward supporting both ChatItem and str (ID), since IDs are already a first-class way to reference items in ChatContext (e.g. get_by_id, index_by_id).

Internally it would just match by item.id in both cases.

Let me know if you’d prefer restricting it to ChatItem only.