feat(rp2040): support RAM-only UF2 loads

[zackees]

Summary

• accept canonical RP2040 UF2 pages targeting main SRAM or XIP-cache SRAM
• reject mixed flash/RAM images, out-of-range pages, wraparound, overlap, and guessed RP2350 RAM layouts
• preserve raw BIN as flash-only
• return a truthful RAM load accepted outcome without waiting for runtime CDC
• use O(n log n) interval validation for large UF2 images

Why

The attached Pico 1 already enters ROM USB, but every flash UF2 stalls on the first erase/program. Raspberry Pi's boot ROM supports RAM UF2 independently of QSPI, making it the decisive transport-vs-flash discriminator.

Validation

• soldr cargo test -p fbuild-deploy: 188 passed, 8 ignored
• soldr cargo clippy -p fbuild-deploy --all-targets -- -D warnings: passed (existing workspace MSRV warning only)
• high-reasoning self-review: clean after replacing an initial quadratic overlap check
• attached Pico 1, fbuild-only: two RAM UF2 cycles detached and re-enumerated RPI-RP2 automatically; DEVPKEY_Device_LastArrivalDate advanced; zero new Windows Disk 51/153 events
• no BOOTSEL press, PC reboot, driver change, PlatformIO deploy, or GPIO

Supports #1049.

Summary by CodeRabbit

• New Features

  • Added support for loading compatible RP2040 images directly into volatile RAM.
  • RAM loads are validated for supported memory regions, alignment, completeness, and overlap issues.
  • Deployment now reports a clear “RAM load accepted” result when non-volatile programming is not performed.

• Bug Fixes

  • Invalid, mixed flash/RAM, incomplete, and overlapping RAM images are now rejected with validation errors.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 1ec4ef39-f9dc-4b9d-9c9e-fb8c2b09eb03

📥 Commits

Reviewing files that changed from the base of the PR and between 209f4b4 and 8f11ff5.

📒 Files selected for processing (2)

• crates/fbuild-deploy/src/lib.rs
• crates/fbuild-deploy/src/rp2040.rs

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📝 Walkthrough

Walkthrough

RP2040 deployment now validates UF2 images as flash or RAM targets. RAM images produce a RamLoad result without non-volatile programming or CDC runtime recovery, while flash images retain the existing deployment path.

Changes

RP2040 RAM deployment

Layer / File(s)	Summary
RAM load outcome contract crates/fbuild-deploy/src/lib.rs	Adds DeployOutcome::RamLoad, documents the expanded outcome set, formats it as "RAM load accepted", and tests the description.
UF2 target classification crates/fbuild-deploy/src/rp2040.rs	Adds RP2040 SRAM address ranges and returns Uf2Target from UF2 validation after checking metadata, target consistency, duplicates, alignment, and overlaps.
RAM deployment branch and coverage crates/fbuild-deploy/src/rp2040.rs	Passes the target through artifact preparation, returns a RAM-load result before CDC handling, and tests valid, mixed, invalid, and overlapping RAM images.

Estimated code review effort: 4 (Complex) | ~45 minutes

Sequence Diagram(s)

sequenceDiagram
  participant DeployMethod
  participant prepare_uf2_artifact
  participant validate_uf2
  participant CDC_Runtime
  DeployMethod->>prepare_uf2_artifact: prepare UF2 artifact
  prepare_uf2_artifact->>validate_uf2: validate and classify UF2
  validate_uf2-->>prepare_uf2_artifact: Uf2Target::Ram or Uf2Target::Flash
  prepare_uf2_artifact-->>DeployMethod: artifact and target
  DeployMethod->>DeployMethod: return RamLoad for RAM target
  DeployMethod->>CDC_Runtime: discover or recover runtime port for flash target

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Possibly related PRs

• FastLED/fbuild#1046: Updates related RP2040 UF2 address mapping and validation logic.
• FastLED/fbuild#1050: Modifies related RP2040 UF2 preparation, validation, and deployment flow behavior.

✨ 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 fix/1049-rp2040-ram-uf2

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