Update Agent/Tool Message Construction and Handling

[RomneyDa]

Description

• Unifies thunks - moves getting system message, constructing messages into the streamNormalInput thunk
• Updates the way dangling messages are cleaned up on stream cancellation - accounts for tool calls, thinking messages, etc.
• Updates message compilation so that fresh tool messages are injected after their tool calls at the time of compiling messages, although output is still streamed to redux toolCallState AND existing tool call messages, so that persisted conversation reflects what is sent to model. This fixes bugs around tool calls not having associated tool messages and vice versa.
• Changes pending tool rejection to just stop rather than continue streaming
• Changes reject diffs after edit tool to stop rather than continue streaming from GUI at least for now
• Removes filtering of tool calls in chat mode (was causing non-sensical history for model) but updates the Bedrock API to insert tool calls and outputs as text parts when the corresponding tool is not in the toolOptions. Updates corresponding tests.
• Changes rule trigger logic to include context items from the most recent user message forward, including tool/assistant messages AFTER the most recent user message (for long agent convos)

Borrows ideas from @chezsmithy #5662

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[RomneyDa]

• Adds a "Truncate chat to this message" icon in non-last tool messages, to allow users to interrupt mid-long agent streams
• Fix bug where toggling mode causes focus loss if not in main editor
• Streamline tool context item to contextItemWithId conversion, add toolCall named icon

EDIT this is no longer relevant

[cubic-dev-ai]

cubic found 2 issues across 9 files. Review them in cubic.dev

_{React with 👍 or 👎 to teach cubic. Tag @cubic-dev-ai to give specific feedback.}

[cubic-dev-ai]

cubic found 5 issues across 22 files. Review them in cubic.dev

_{React with 👍 or 👎 to teach cubic. Tag @cubic-dev-ai to give specific feedback.}

[sestinj]

It feels like there's a chance this could have been 2 PRs? I don't know exactly what the order of operations looked like while you were working on it, but just noting that this was slightly messy to review

Otherwise biggest thing is unit tests on constructMessages

And make sure to take a look at Cubic's feedback. At least the gap one is accurate