feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/litrs/src/string/mod.rs

@@ -0,0 +1,129 @@
+use std::{fmt, ops::Range};
+
+use crate::{
+    err::{perr, ParseErrorKind::*},
+    escape::{scan_raw_string, unescape_string},
+    parse::first_byte_or_empty,
+    Buffer, ParseError,
+};
+
+
+/// A string or raw string literal, e.g. `"foo"`, `"Grüße"` or `r#"a🦊c"d🦀f"#`.
+///
+/// See [the reference][ref] for more information.
+///
+/// [ref]: https://doc.rust-lang.org/reference/tokens.html#string-literals
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct StringLit<B: Buffer> {
+    /// The raw input.
+    raw: B,
+
+    /// The string value (with all escapes unescaped), or `None` if there were
+    /// no escapes. In the latter case, the string value is in `raw`.
+    value: Option<String>,
+
+    /// The number of hash signs in case of a raw string literal, or `None` if
+    /// it's not a raw string literal.
+    num_hashes: Option<u8>,
+
+    /// Start index of the suffix or `raw.len()` if there is no suffix.
+    start_suffix: usize,
+}
+
+impl<B: Buffer> StringLit<B> {
+    /// Parses the input as a (raw) string literal. Returns an error if the
+    /// input is invalid or represents a different kind of literal.
+    pub fn parse(input: B) -> Result<Self, ParseError> {
+        match first_byte_or_empty(&input)? {
+            b'r' | b'"' => {
+                let (value, num_hashes, start_suffix) = parse_impl(&input)?;
+                Ok(Self { raw: input, value, num_hashes, start_suffix })
+            }
+            _ => Err(perr(0, InvalidStringLiteralStart)),
+        }
+    }
+
+    /// Returns the string value this literal represents (where all escapes have
+    /// been turned into their respective values).
+    pub fn value(&self) -> &str {
+        self.value
+            .as_deref()
+            .unwrap_or(&self.raw[self.inner_range()])
+    }
+
+    /// Like `value` but returns a potentially owned version of the value.
+    ///
+    /// The return value is either `String` if `B = String`, or
+    /// `Cow<'a, str>` if `B = &'a str`.
+    pub fn into_value(self) -> B::Cow {
+        let inner_range = self.inner_range();
+        let Self { raw, value, .. } = self;
+        value
+            .map(B::Cow::from)
+            .unwrap_or_else(|| raw.cut(inner_range).into_cow())
+    }
+
+    /// The optional suffix. Returns `""` if the suffix is empty/does not exist.
+    pub fn suffix(&self) -> &str {
+        &(*self.raw)[self.start_suffix..]
+    }
+
+    /// Returns whether this literal is a raw string literal (starting with
+    /// `r`).
+    pub fn is_raw_string(&self) -> bool {
+        self.num_hashes.is_some()
+    }
+
+    /// Returns the raw input that was passed to `parse`.
+    pub fn raw_input(&self) -> &str {
+        &self.raw
+    }
+
+    /// Returns the raw input that was passed to `parse`, potentially owned.
+    pub fn into_raw_input(self) -> B {
+        self.raw
+    }
+
+    /// The range within `self.raw` that excludes the quotes and potential `r#`.
+    fn inner_range(&self) -> Range<usize> {
+        match self.num_hashes {
+            None => 1..self.start_suffix - 1,
+            Some(n) => 1 + n as usize + 1..self.start_suffix - n as usize - 1,
+        }
+    }
+}
+
+impl StringLit<&str> {
+    /// Makes a copy of the underlying buffer and returns the owned version of
+    /// `Self`.
+    pub fn into_owned(self) -> StringLit<String> {
+        StringLit {
+            raw: self.raw.to_owned(),
+            value: self.value,
+            num_hashes: self.num_hashes,
+            start_suffix: self.start_suffix,
+        }
+    }
+}
+
+impl<B: Buffer> fmt::Display for StringLit<B> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad(&self.raw)
+    }
+}
+
+/// Precondition: input has to start with either `"` or `r`.
+#[inline(never)]
+pub(crate) fn parse_impl(input: &str) -> Result<(Option<String>, Option<u8>, usize), ParseError> {
+    if input.starts_with('r') {
+        scan_raw_string(input, 1, true, true)
+            .map(|(hashes, start_suffix)| (None, Some(hashes), start_suffix))
+    } else {
+        unescape_string::<String>(input, 1, true, false, true)
+            .map(|(v, start_suffix)| (v, None, start_suffix))
+    }
+}
+
+
+#[cfg(test)]
+mod tests;

vendor/litrs/src/string/tests.rs

@@ -0,0 +1,262 @@
+use crate::{
+    test_util::{assert_parse_ok_eq, assert_roundtrip},
+    Literal, StringLit,
+};
+
+// ===== Utility functions =======================================================================
+
+macro_rules! check {
+    ($lit:literal, $has_escapes:expr, $num_hashes:expr) => {
+        check!($lit, stringify!($lit), $has_escapes, $num_hashes, "")
+    };
+    ($lit:literal, $input:expr, $has_escapes:expr, $num_hashes:expr, $suffix:literal) => {
+        let input = $input;
+        let expected = StringLit {
+            raw: input,
+            value: if $has_escapes { Some($lit.to_string()) } else { None },
+            num_hashes: $num_hashes,
+            start_suffix: input.len() - $suffix.len(),
+        };
+
+        assert_parse_ok_eq(input, StringLit::parse(input), expected.clone(), "StringLit::parse");
+        assert_parse_ok_eq(
+            input, Literal::parse(input), Literal::String(expected.clone()), "Literal::parse");
+        let lit = StringLit::parse(input).unwrap();
+        assert_eq!(lit.value(), $lit);
+        assert_eq!(lit.suffix(), $suffix);
+        assert_eq!(lit.into_value(), $lit);
+        assert_roundtrip(expected.into_owned(), input);
+    };
+}
+
+
+// ===== Actual tests ============================================================================
+
+#[test]
+fn simple() {
+    check!("", false, None);
+    check!("a", false, None);
+    check!("peter", false, None);
+    check!("Sei gegrüßt, Bärthelt!", false, None);
+    check!("أنا لا أتحدث العربية", false, None);
+    check!("お前はもう死んでいる", false, None);
+    check!("Пушки - интересные музыкальные инструменты", false, None);
+    check!("lit 👌 😂 af", false, None);
+}
+
+#[test]
+fn special_whitespace() {
+    let strings = ["\n", "\t", "foo\tbar", "🦊\n"];
+
+    for &s in &strings {
+        let input = format!(r#""{}""#, s);
+        let input_raw = format!(r#"r"{}""#, s);
+        for (input, num_hashes) in vec![(input, None), (input_raw, Some(0))] {
+            let expected = StringLit {
+                raw: &*input,
+                value: None,
+                num_hashes,
+                start_suffix: input.len(),
+            };
+            assert_parse_ok_eq(
+                &input, StringLit::parse(&*input), expected.clone(), "StringLit::parse");
+            assert_parse_ok_eq(
+                &input, Literal::parse(&*input), Literal::String(expected), "Literal::parse");
+            assert_eq!(StringLit::parse(&*input).unwrap().value(), s);
+            assert_eq!(StringLit::parse(&*input).unwrap().into_value(), s);
+        }
+    }
+}
+
+#[test]
+fn simple_escapes() {
+    check!("a\nb", true, None);
+    check!("\nb", true, None);
+    check!("a\n", true, None);
+    check!("\n", true, None);
+
+    check!("\x60犬 \t 猫\r馬\n うさぎ \0ネズミ", true, None);
+    check!("నా \\పిల్లి లావుగా ఉంది", true, None);
+    check!("నా \\పిల్లి లావుగా 🐈\"ఉంది", true, None);
+    check!("\\నా\\ పిల్లి లావుగా\" ఉంది\"", true, None);
+    check!("\"నా \\🐈 పిల్లి లావుగా \" ఉంది\\", true, None);
+
+    check!("\x00", true, None);
+    check!(" \x01", true, None);
+    check!("\x0c 🦊", true, None);
+    check!(" 🦊\x0D ", true, None);
+    check!("\\x13", true, None);
+    check!("\"x30", true, None);
+}
+
+#[test]
+fn unicode_escapes() {
+    check!("\u{0}", true, None);
+    check!(" \u{00}", true, None);
+    check!("\u{b} ", true, None);
+    check!(" \u{B} ", true, None);
+    check!("\u{7e}", true, None);
+    check!("నక్క\u{E4}", true, None);
+    check!("\u{e4} నక్క", true, None);
+    check!(" \u{fc}నక్క ", true, None);
+    check!("\u{Fc}", true, None);
+    check!("\u{fC}🦊\nлиса", true, None);
+    check!("лиса\u{FC}", true, None);
+    check!("лиса\u{b10}నక్క🦊", true, None);
+    check!("\"నక్క\u{B10}", true, None);
+    check!("лиса\\\u{0b10}", true, None);
+    check!("ли🦊са\\\"\u{0b10}", true, None);
+    check!("నక్క\\\\u{0b10}", true, None);
+    check!("\u{2764}Füchsin", true, None);
+    check!("Füchse \u{1f602}", true, None);
+    check!("cd\u{1F602}ab", true, None);
+
+    check!("\u{0}🦊", true, None);
+    check!("лиса\u{0__}", true, None);
+    check!("\\🦊\u{3_b}", true, None);
+    check!("🦊\u{1_F_6_0_2}Füchsin", true, None);
+    check!("నక్క\\\u{1_F6_02_____}నక్క", true, None);
+
+    check!("a\u{7e}b\u{fc}c\u{0b10}d", true, None);
+}
+
+#[test]
+fn string_continue() {
+    check!("నక్క\
+        bar", true, None);
+    check!("foo\
+🦊", true, None);
+
+    check!("foo\
+
+        banana", true, None);
+
+    // Weird whitespace characters
+    let lit = StringLit::parse("\"foo\\\n\t\n \n\tbar\"").expect("failed to parse");
+    assert_eq!(lit.value(), "foobar");
+    let lit = StringLit::parse("\"foo\\\n\u{85}bar\"").expect("failed to parse");
+    assert_eq!(lit.value(), "foo\u{85}bar");
+    let lit = StringLit::parse("\"foo\\\n\u{a0}bar\"").expect("failed to parse");
+    assert_eq!(lit.value(), "foo\u{a0}bar");
+
+    // Raw strings do not handle "string continues"
+    check!(r"foo\
+        bar", false, Some(0));
+}
+
+#[test]
+fn raw_string() {
+    check!(r"", false, Some(0));
+    check!(r"a", false, Some(0));
+    check!(r"peter", false, Some(0));
+    check!(r"Sei gegrüßt, Bärthelt!", false, Some(0));
+    check!(r"أنا لا أتحدث العربية", false, Some(0));
+    check!(r"お前はもう死んでいる", false, Some(0));
+    check!(r"Пушки - интересные музыкальные инструменты", false, Some(0));
+    check!(r"lit 👌 😂 af", false, Some(0));
+
+    check!(r#""#, false, Some(1));
+    check!(r#"a"#, false, Some(1));
+    check!(r##"peter"##, false, Some(2));
+    check!(r###"Sei gegrüßt, Bärthelt!"###, false, Some(3));
+    check!(r########"lit 👌 😂 af"########, false, Some(8));
+
+    check!(r#"foo " bar"#, false, Some(1));
+    check!(r##"foo " bar"##, false, Some(2));
+    check!(r#"foo """" '"'" bar"#, false, Some(1));
+    check!(r#""foo""#, false, Some(1));
+    check!(r###""foo'"###, false, Some(3));
+    check!(r#""x'#_#s'"#, false, Some(1));
+    check!(r"#", false, Some(0));
+    check!(r"foo#", false, Some(0));
+    check!(r"##bar", false, Some(0));
+    check!(r###""##foo"##bar'"###, false, Some(3));
+
+    check!(r"さび\n\t\r\0\\x60\u{123}フェリス", false, Some(0));
+    check!(r#"さび\n\t\r\0\\x60\u{123}フェリス"#, false, Some(1));
+}
+
+#[test]
+fn suffixes() {
+    check!("hello", r###""hello"suffix"###, false, None, "suffix");
+    check!(r"お前はもう死んでいる", r###"r"お前はもう死んでいる"_banana"###, false, Some(0), "_banana");
+    check!("fox", r#""fox"peter"#, false, None, "peter");
+    check!("🦊", r#""🦊"peter"#, false, None, "peter");
+    check!("నక్క\\\\u{0b10}", r###""నక్క\\\\u{0b10}"jü_rgen"###, true, None, "jü_rgen");
+}
+
+#[test]
+fn parse_err() {
+    assert_err!(StringLit, r#"""#, UnterminatedString, None);
+    assert_err!(StringLit, r#""犬"#, UnterminatedString, None);
+    assert_err!(StringLit, r#""Jürgen"#, UnterminatedString, None);
+    assert_err!(StringLit, r#""foo bar baz"#, UnterminatedString, None);
+
+    assert_err!(StringLit, r#""fox"peter""#, InvalidSuffix, 5);
+    assert_err!(StringLit, r###"r#"foo "# bar"#"###, UnexpectedChar, 9);
+
+    assert_err!(StringLit, "\"\r\"", CarriageReturn, 1);
+    assert_err!(StringLit, "\"fo\rx\"", CarriageReturn, 3);
+    assert_err!(StringLit, "r\"\r\"", CarriageReturn, 2);
+    assert_err!(StringLit, "r\"fo\rx\"", CarriageReturn, 4);
+
+    assert_err!(StringLit, r##"r####""##, UnterminatedRawString, None);
+    assert_err!(StringLit, r#####"r##"foo"#bar"#####, UnterminatedRawString, None);
+    assert_err!(StringLit, r##"r####"##, InvalidLiteral, None);
+    assert_err!(StringLit, r##"r####x"##, InvalidLiteral, None);
+}
+
+#[test]
+fn invald_ascii_escapes() {
+    assert_err!(StringLit, r#""\x80""#, NonAsciiXEscape, 1..5);
+    assert_err!(StringLit, r#""🦊\x81""#, NonAsciiXEscape, 5..9);
+    assert_err!(StringLit, r#"" \x8a""#, NonAsciiXEscape, 2..6);
+    assert_err!(StringLit, r#""\x8Ff""#, NonAsciiXEscape, 1..5);
+    assert_err!(StringLit, r#""\xa0 ""#, NonAsciiXEscape, 1..5);
+    assert_err!(StringLit, r#""నక్క\xB0""#, NonAsciiXEscape, 13..17);
+    assert_err!(StringLit, r#""\xc3నక్క""#, NonAsciiXEscape, 1..5);
+    assert_err!(StringLit, r#""\xDf🦊""#, NonAsciiXEscape, 1..5);
+    assert_err!(StringLit, r#""నక్క\xffనక్క""#, NonAsciiXEscape, 13..17);
+    assert_err!(StringLit, r#""\xfF ""#, NonAsciiXEscape, 1..5);
+    assert_err!(StringLit, r#"" \xFf""#, NonAsciiXEscape, 2..6);
+    assert_err!(StringLit, r#""నక్క  \xFF""#, NonAsciiXEscape, 15..19);
+}
+
+#[test]
+fn invalid_escapes() {
+    assert_err!(StringLit, r#""\a""#, UnknownEscape, 1..3);
+    assert_err!(StringLit, r#""foo\y""#, UnknownEscape, 4..6);
+    assert_err!(StringLit, r#""\"#, UnterminatedEscape, 1);
+    assert_err!(StringLit, r#""\x""#, UnterminatedEscape, 1..3);
+    assert_err!(StringLit, r#""🦊\x1""#, UnterminatedEscape, 5..8);
+    assert_err!(StringLit, r#"" \xaj""#, InvalidXEscape, 2..6);
+    assert_err!(StringLit, r#""నక్క\xjb""#, InvalidXEscape, 13..17);
+}
+
+#[test]
+fn invalid_unicode_escapes() {
+    assert_err!(StringLit, r#""\u""#, UnicodeEscapeWithoutBrace, 1..3);
+    assert_err!(StringLit, r#""🦊\u ""#, UnicodeEscapeWithoutBrace, 5..7);
+    assert_err!(StringLit, r#""\u3""#, UnicodeEscapeWithoutBrace, 1..3);
+
+    assert_err!(StringLit, r#""\u{""#, UnterminatedUnicodeEscape, 1..4);
+    assert_err!(StringLit, r#""\u{12""#, UnterminatedUnicodeEscape, 1..6);
+    assert_err!(StringLit, r#""🦊\u{a0b""#, UnterminatedUnicodeEscape, 5..11);
+    assert_err!(StringLit, r#""\u{a0_b  ""#, UnterminatedUnicodeEscape, 1..10);
+
+    assert_err!(StringLit, r#""\u{_}నక్క""#, InvalidStartOfUnicodeEscape, 4);
+    assert_err!(StringLit, r#""\u{_5f}""#, InvalidStartOfUnicodeEscape, 4);
+
+    assert_err!(StringLit, r#""fox\u{x}""#, NonHexDigitInUnicodeEscape, 7);
+    assert_err!(StringLit, r#""\u{0x}🦊""#, NonHexDigitInUnicodeEscape, 5);
+    assert_err!(StringLit, r#""నక్క\u{3bx}""#, NonHexDigitInUnicodeEscape, 18);
+    assert_err!(StringLit, r#""\u{3b_x}лиса""#, NonHexDigitInUnicodeEscape, 7);
+    assert_err!(StringLit, r#""\u{4x_}""#, NonHexDigitInUnicodeEscape, 5);
+
+    assert_err!(StringLit, r#""\u{1234567}""#, TooManyDigitInUnicodeEscape, 10);
+    assert_err!(StringLit, r#""నక్క\u{1234567}🦊""#, TooManyDigitInUnicodeEscape, 22);
+    assert_err!(StringLit, r#""నక్క\u{1_23_4_56_7}""#, TooManyDigitInUnicodeEscape, 26);
+    assert_err!(StringLit, r#""\u{abcdef123}лиса""#, TooManyDigitInUnicodeEscape, 10);
+
+    assert_err!(StringLit, r#""\u{110000}fox""#, InvalidUnicodeEscapeChar, 1..11);
+}