toolchain: bump pinned Rust 1.80 → 1.85 (edition 2024 floor)

uuid 1.x → getrandom 0.4.x requires edition = "2024", stabilized in Rust 1.85.
The Task 1 pin of 1.80 was written when uuid 1.x resolved to a getrandom that
still compiled on edition 2021; the resolution has shifted. The brief said
'confirm the latest stable at impl time' — bumping the pin is faithful to that.

Plan doc's Task 6 CI matrix also updated: [stable, "1.85"].

Cross-task correction in response to Task 2 implementer's DONE_WITH_CONCERNS
escalation; not a Task 2 code change.

docs/superpowers/plans/2026-06-28-slice-1-webrtc-loopback.md

@@ -162,12 +162,12 @@ tower = { version = "0.5", features = ["util"] }
 
 - [ ] **Step 2: Write `rust-toolchain.toml`**
 
-Pin stable (currently 1.80 as of writing — confirm the latest stable at impl time with `rustc --version`). The MSRV is whatever str0m 0.21 requires; the CI matrix (Task 6) tests stable + MSRV.
+Pin stable (currently 1.85 as of writing — bumped from 1.80 because `uuid 1.x → getrandom 0.4.x` requires Rust `edition = "2024"`, stabilized in 1.85. Confirm the latest stable at impl time with `rustc --version`). The MSRV is the edition-2024 floor; the CI matrix (Task 6) tests stable + MSRV.
 
 ```toml
 # rust-toolchain.toml — pins the toolchain for reproducible builds.
 [toolchain]
-channel = "1.80"
+channel = "1.85"
 components = ["rustfmt", "clippy"]
 ```
 
@@ -2352,7 +2352,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        toolchain: [stable, "1.80"]
+        toolchain: [stable, "1.85"]
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
@@ -2402,7 +2402,7 @@ deny.toml allows the permissive Rust-ecosystem licenses + our own
 GPL-3.0-or-later; bans duplicate versions of tokio/serde/bytes/tracing
 to catch dep-tree divergence early; restricts sources to crates.io. CI
 runs fmt --check, clippy -D warnings, test --all (matrix: stable +
-MSRV 1.80), and cargo deny check on push + PR to main. The CI job
+MSRV 1.85), and cargo deny check on push + PR to main. The CI job
 installs libopus-dev — the opus crate's FFI dependency (PORT_PLAN §7
 'Core (FFI)' disposition)."
 ```

rust-toolchain.toml

@@ -1,4 +1,4 @@
 # rust-toolchain.toml — pins the toolchain for reproducible builds.
 [toolchain]
-channel = "1.80"
+channel = "1.85"
 components = ["rustfmt", "clippy"]