feat: add message module

[bobrykov]

Summary by CodeRabbit

• New Features

  • Comprehensive messaging framework for agent interactions with user and assistant roles
  • Messages now support multiple content types: text, images (base64), tool calls, and multipart tool results
  • Human-readable display formatting for messages, roles, and tool results
  • Built-in serialization/deserialization for all message and result types

• Chores

  • Library crate name updated to "loopctl"

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: defaults

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Run ID: f0c89dac-36a5-4b44-9b3d-261d76d7e662

📥 Commits

Reviewing files that changed from the base of the PR and between 17c50af and 10f39dc.

📒 Files selected for processing (3)

• Cargo.toml
• src/lib.rs
• src/message.rs

✅ Files skipped from review due to trivial changes (1)

• src/lib.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• src/message.rs

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📝 Walkthrough

Walkthrough

Adds a new serializable conversation schema and related types (Message, MessagePart, Role, ToolResult, ImageSource) with constructors, Display impls, serde support, unit tests, and exports the message module from the crate root. Also renames the library in Cargo.toml from agentloop to loopctl.

Changes

Agent Message Framework

Layer / File(s)	Summary
Data Shape src/message.rs	Adds Message { role: Role, parts: Vec<MessagePart> }, Role enum (user/assistant), and MessagePart tagged enum variants (Text, Image, ToolCall, ToolResult) with serde derives.
Tool & Image Types src/message.rs	Adds ImageSource (base64 encoding via new_base64), ToolResult (untagged: Text or Multipart), and ToolResultPart (text/image) with constructors and serde rules.
Methods & Predicates src/message.rs	Implements constructors and helpers: Message::user/assistant/new, MessagePart::text/tool_call/tool_result, ToolResult::from_string/from_multipart, and predicates/accessors (is_text, is_tool_call, is_tool_result, as_text, is_string).
Display & Formatting src/message.rs	Implements fmt::Display for Message, Role, and ToolResult; renders parts line-by-line, serializes tool-call input to JSON when possible, formats tool results and images human-readably.
Tests / Validation src/message.rs	Adds unit tests covering constructors, predicates, ImageSource::new_base64, ToolResult conversions/display, and serde JSON round-trips for Message and Vec<MessagePart>.
Crate Export / Docs src/lib.rs	Replaces crate-level placeholder docs with module documentation describing the trait-based agent-loop framework and publicly exports pub mod message;.
Manifest Cargo.toml	Updates [lib].name from agentloop to loopctl.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Poem

🐇 I hopped through structs, parts, and a test,

Base64 carrots tucked in my nest.
Tools chat and images gleam, neat and bright—
Messages line up, ready for flight.
— your rabbit, nibbling code by moonlight

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: add message module' directly and accurately describes the main change: introducing a new message module with conversation message schema and related types.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/add-message

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@src/message.rs`:
- Around line 350-353: The doc comment references a non-existent intra-doc link
`crate::stream::DeltaContent::Text`; update the comment in src/message.rs to
remove the intra-doc link and use plain code text instead (e.g.,
DeltaContent::Text) so rustdoc stops resolving `crate::stream`. Locate the
comment around the doc for the assembled text and replace the `[`...`]` link
(`[`DeltaContent::Text`](crate::stream::DeltaContent::Text)`) with an inline
code mention like DeltaContent::Text.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: af503b73-c0db-4a2c-a245-9a2e676b719b

📥 Commits

Reviewing files that changed from the base of the PR and between 2c6709a and df1b609.

📒 Files selected for processing (2)

• src/lib.rs
• src/message.rs