refactor(repl): split help.go into data (help_topics.go) and logic (help.go)

The original help.go was 657 lines mixing data, indexing, and lookup
logic. Split into:

- help_topics.go (489 lines): HelpTopic struct, helpTopics data slice,
  index variables, and init() that builds the lookup maps.
- help.go (171 lines): GetHelp, GetAllTopics, GetCompletionTopics,
  getGeneralHelp, getCategoriesHelp, and formatTopic.

All tests pass. No behavioral changes.

2 files changed, 489 insertions, 486 deletions

diff --git a/internal/repl/help.go b/internal/repl/help.go
index 1aaec09..02688e1 100644
--- a/internal/repl/help.go
+++ b/internal/repl/help.go
@@ -9,492 +9,6 @@ import (
 	"strings"
 )
 
-// HelpTopic holds the inline help content for one operator, function, or REPL command.
-type HelpTopic struct {
-	Category   string // e.g. "Arithmetic", "Stack", "Comparison", "Variables", "Hyper", "REPL"
-	Operator   string // the operator or command name (e.g. "+", "help", "rat")
-	Aliases    []string
-	Description string
-	Usage      string // short usage hint
-	Examples   []string
-}
-
-// helpTopics is the single source of truth for all inline help entries.
-// Each entry documents one operator, function, or REPL command with examples.
-var helpTopics = []HelpTopic{
-	// ── REPL commands ──
-
-	{
-		Category:    "REPL",
-		Operator:    "help",
-		Description: "Show help information",
-		Usage:       "help [topic]",
-		Examples: []string{
-			"help              Show general help overview",
-			"help +            Show help for the + operator",
-			"help dup          Show help for dup",
-		},
-	},
-	{
-		Category:    "REPL",
-		Operator:    "clear",
-		Description: "Clear the terminal screen",
-		Usage:       "clear",
-		Examples: []string{
-			"clear",
-		},
-	},
-	{
-		Category:    "REPL",
-		Operator:    "quit",
-		Aliases:     []string{"exit"},
-		Description: "Exit the REPL",
-		Usage:       "quit or exit",
-		Examples: []string{
-			"quit",
-		},
-	},
-	{
-		Category:    "REPL",
-		Operator:    "rpn",
-		Aliases:     []string{"calc"},
-		Description: "Evaluate an RPN (Reverse Polish Notation) expression",
-		Usage:       "rpn <expression>",
-		Examples: []string{
-			"rpn 3 4 +         Evaluate 3 + 4 = 7",
-			"rpn 10 2 /        Evaluate 10 / 2 = 5",
-			"calc 5 3 *        Same as 'rpn 5 3 *'",
-		},
-	},
-	{
-		Category:    "REPL",
-		Operator:    "rat",
-		Description: "Switch between float64 and rational number modes",
-		Usage:       "rat on|off|toggle",
-		Examples: []string{
-			"rat on      Enable rational mode",
-			"rat off     Disable rational mode (float64)",
-			"rat toggle  Toggle between modes",
-		},
-	},
-	{
-		Category:    "REPL",
-		Operator:    "stack",
-		Description: "Show current RPN stack state",
-		Usage:       "stack",
-		Examples: []string{
-			"1 2 3 stack     Show stack: 1 2 3",
-		},
-	},
-
-	// ── Arithmetic operators ──
-
-	{
-		Category:    "Arithmetic",
-		Operator:    "+",
-		Description: "Add two numbers (metric-aware)",
-		Usage:       "a b +",
-		Examples: []string{
-			"3 4 +           3 + 4 = 7",
-			"100Mbps 50 +    100Mbps + 50Mbps = 150Mbps (Cool absorbs metric)",
-		},
-	},
-	{
-		Category:    "Arithmetic",
-		Operator:    "-",
-		Description: "Subtract two numbers (metric-aware)",
-		Usage:       "a b -",
-		Examples: []string{
-			"10 3 -          10 - 3 = 7",
-			"200Mbps 50 -    200Mbps - 50Mbps = 150Mbps",
-		},
-	},
-	{
-		Category:    "Arithmetic",
-		Operator:    "*",
-		Description: "Multiply two numbers",
-		Usage:       "a b *",
-		Examples: []string{
-			"3 4 *           3 * 4 = 12",
-			"100Mbps 2 *     100Mbps * 2 = 200Mbps (Cool preserves metric)",
-		},
-	},
-	{
-		Category:    "Arithmetic",
-		Operator:    "/",
-		Description: "Divide two numbers (a / b)",
-		Usage:       "a b /",
-		Examples: []string{
-			"10 3 /          10 / 3 = 3.333...",
-		},
-	},
-	{
-		Category:    "Arithmetic",
-		Operator:    "^",
-		Description: "Raise to power (a ^ b), result is always unitless",
-		Usage:       "a b ^",
-		Examples: []string{
-			"2 3 ^           2 ^ 3 = 8",
-			"10 0.5 ^        10 ^ 0.5 = sqrt(10) = 3.162...",
-		},
-	},
-	{
-		Category:    "Arithmetic",
-		Operator:    "**",
-		Description: "Raise to integer power (a ** b) using fast binary exponentiation",
-		Usage:       "a b **",
-		Examples: []string{
-			"2 10 **         2 ^ 10 = 1024",
-			"3 6 **          3 ^ 6 = 729",
-		},
-	},
-	{
-		Category:    "Arithmetic",
-		Operator:    "%",
-		Description: "Modulo (remainder of a / b)",
-		Usage:       "a b %",
-		Examples: []string{
-			"10 3 %          10 mod 3 = 1",
-			"7 2 %           7 mod 2 = 1",
-		},
-	},
-	{
-		Category:    "Arithmetic",
-		Operator:    "lg",
-		Description: "Logarithm base 2",
-		Usage:       "a lg",
-		Examples: []string{
-			"8 lg            log2(8) = 3",
-			"1024 lg         log2(1024) = 10",
-		},
-	},
-	{
-		Category:    "Arithmetic",
-		Operator:    "log",
-		Description: "Logarithm base 10",
-		Usage:       "a log",
-		Examples: []string{
-			"100 log         log10(100) = 2",
-			"1000 log        log10(1000) = 3",
-		},
-	},
-	{
-		Category:    "Arithmetic",
-		Operator:    "ln",
-		Description: "Natural logarithm (base e)",
-		Usage:       "a ln",
-		Examples: []string{
-			"2.71828 ln      ln(2.71828) ~= 1",
-			"1 ln            ln(1) = 0",
-		},
-	},
-
-	// ── Comparison operators ──
-
-	{
-		Category:    "Comparison",
-		Operator:    ">",
-		Aliases:     []string{"gt"},
-		Description: "Greater than: pushes true (1) or false (0)",
-		Usage:       "a b >",
-		Examples: []string{
-			"5 3 >           5 > 3 = true (1)",
-			"3 5 >           3 > 5 = false (0)",
-		},
-	},
-	{
-		Category:    "Comparison",
-		Operator:    "<",
-		Aliases:     []string{"lt"},
-		Description: "Less than: pushes true (1) or false (0)",
-		Usage:       "a b <",
-		Examples: []string{
-			"3 5 <           3 < 5 = true (1)",
-			"5 3 <           5 < 3 = false (0)",
-		},
-	},
-	{
-		Category:    "Comparison",
-		Operator:    ">=",
-		Aliases:     []string{"gte"},
-		Description: "Greater than or equal: pushes true (1) or false (0)",
-		Usage:       "a b >=",
-		Examples: []string{
-			"5 5 >=          5 >= 5 = true (1)",
-			"3 5 >=          3 >= 5 = false (0)",
-		},
-	},
-	{
-		Category:    "Comparison",
-		Operator:    "<=",
-		Aliases:     []string{"lte"},
-		Description: "Less than or equal: pushes true (1) or false (0)",
-		Usage:       "a b <=",
-		Examples: []string{
-			"3 3 <=          3 <= 3 = true (1)",
-			"5 3 <=          5 <= 3 = false (0)",
-		},
-	},
-	{
-		Category:    "Comparison",
-		Operator:    "==",
-		Aliases:     []string{"eq"},
-		Description: "Equal: pushes true (1) or false (0)",
-		Usage:       "a b ==",
-		Examples: []string{
-			"5 5 ==          5 == 5 = true (1)",
-			"5 3 ==          5 == 3 = false (0)",
-		},
-	},
-	{
-		Category:    "Comparison",
-		Operator:    "!=",
-		Aliases:     []string{"neq"},
-		Description: "Not equal: pushes true (1) or false (0)",
-		Usage:       "a b !=",
-		Examples: []string{
-			"5 3 !=          5 != 3 = true (1)",
-			"5 5 !=          5 != 5 = false (0)",
-		},
-	},
-
-	// ── Stack operators ──
-
-	{
-		Category:    "Stack",
-		Operator:    "dup",
-		Description: "Duplicate the top stack value",
-		Usage:       "a dup",
-		Examples: []string{
-			"5 dup           Stack: 5 5",
-			"3 dup dup       Stack: 3 3 3",
-		},
-	},
-	{
-		Category:    "Stack",
-		Operator:    "swap",
-		Description: "Swap the top two stack values",
-		Usage:       "a b swap",
-		Examples: []string{
-			"1 2 swap        Stack: 2 1",
-		},
-	},
-	{
-		Category:    "Stack",
-		Operator:    "pop",
-		Description: "Remove and discard the top stack value",
-		Usage:       "pop",
-		Examples: []string{
-			"1 2 3 pop       Stack: 1 2",
-		},
-	},
-	{
-		Category:    "Stack",
-		Operator:    "d",
-		Description: "Pop a symbol from stack and delete that variable",
-		Usage:       ":x d",
-		Examples: []string{
-			":x d            Delete variable x",
-		},
-	},
-	{
-		Category:    "Stack",
-		Operator:    "show",
-		Aliases:     []string{"showstack", "print"},
-		Description: "Display the current stack contents",
-		Usage:       "show",
-		Examples: []string{
-			"1 2 3 show      Prints: 1 2 3",
-			"show            Prints: Stack is empty",
-		},
-	},
-
-	// ── Variable operators ──
-
-	{
-		Category:    "Variables",
-		Operator:    ":=",
-		Description: "Assign value to variable (name on bottom, value on top)",
-		Usage:       ":name value :=",
-		Examples: []string{
-			":x 5 :=         Set variable x to 5",
-			":y 3.14 :=      Set variable y to 3.14",
-		},
-	},
-	{
-		Category:    "Variables",
-		Operator:    "=:",
-		Description: "Assign value to variable (value on bottom, name on top)",
-		Usage:       "value :name =:",
-		Examples: []string{
-			"5 :x =:         Set variable x to 5",
-		},
-	},
-	{
-		Category:    "Variables",
-		Operator:    "vars",
-		Description: "List all defined variables and their values",
-		Usage:       "vars",
-		Examples: []string{
-			"vars            List all variables",
-		},
-	},
-	{
-		Category:    "Variables",
-		Operator:    "clear",
-		Description: "Clear all user-defined variables",
-		Usage:       "clear",
-		Examples: []string{
-			"clear           Remove all variables",
-		},
-	},
-	{
-		Category:    "Variables",
-		Operator:    "convert",
-		Description: "Convert a value to a target metric (@X syntax)",
-		Usage:       "value @target convert",
-		Examples: []string{
-			"100Mbps @bps convert    Convert 100Mbps to bps",
-		},
-	},
-
-	// ── Constants ──
-
-	{
-		Category:    "Constants",
-		Operator:    "constants",
-		Description: "List all available constants",
-		Usage:       "constants",
-		Examples: []string{
-			"constants       List all built-in constants",
-		},
-	},
-	{
-		Category:    "Constants",
-		Operator:    "clearconstants",
-		Description: "Reset all constants to built-in defaults",
-		Usage:       "clearconstants",
-		Examples: []string{
-			"clearconstants  Reset constants",
-		},
-	},
-
-	// ── Hyper (n-ary) operators ──
-
-	{
-		Category:    "Hyper",
-		Operator:    "[+]",
-		Description: "Add all stack values together (n-ary)",
-		Usage:       "a b c [+] ...",
-		Examples: []string{
-			"1 2 3 [+]       1 + 2 + 3 = 6",
-			"10 20 30 40 [+] 100",
-		},
-	},
-	{
-		Category:    "Hyper",
-		Operator:    "[-]",
-		Description: "Subtract all stack values left-associative (n-ary)",
-		Usage:       "a b c [-] ...",
-		Examples: []string{
-			"10 3 2 [-]      10 - 3 - 2 = 5",
-		},
-	},
-	{
-		Category:    "Hyper",
-		Operator:    "[*]",
-		Description: "Multiply all stack values together (n-ary)",
-		Usage:       "a b c [*] ...",
-		Examples: []string{
-			"2 3 4 [*]       2 * 3 * 4 = 24",
-		},
-	},
-	{
-		Category:    "Hyper",
-		Operator:    "[/]",
-		Description: "Divide all stack values left-associative (n-ary)",
-		Usage:       "a b c [/] ...",
-		Examples: []string{
-			"100 2 5 [/]     100 / 2 / 5 = 10",
-		},
-	},
-	{
-		Category:    "Hyper",
-		Operator:    "[^]",
-		Description: "Power all stack values left-associative (n-ary)",
-		Usage:       "a b c [^] ...",
-		Examples: []string{
-			"2 3 2 [^]       2 ^ 3 ^ 2 = 8",
-		},
-	},
-	{
-		Category:    "Hyper",
-		Operator:    "[%]",
-		Description: "Modulo all stack values left-associative (n-ary)",
-		Usage:       "a b c [%] ...",
-		Examples: []string{
-			"100 10 3 [%]    100 % 10 % 3 = 1",
-		},
-	},
-	{
-		Category:    "Hyper",
-		Operator:    "[lg]",
-		Description: "Sum of log2 of all stack values (n-ary)",
-		Usage:       "a b [lg] ...",
-		Examples: []string{
-			"2 4 [lg]        log2(2) + log2(4) = 1 + 2 = 3",
-		},
-	},
-	{
-		Category:    "Hyper",
-		Operator:    "[log]",
-		Description: "Sum of log10 of all stack values (n-ary)",
-		Usage:       "a b [log] ...",
-		Examples: []string{
-			"10 100 [log]    log10(10) + log10(100) = 1 + 2 = 3",
-		},
-	},
-	{
-		Category:    "Hyper",
-		Operator:    "[ln]",
-		Description: "Sum of natural log of all stack values (n-ary)",
-		Usage:       "a b [ln] ...",
-		Examples: []string{
-			"1 2.71828 [ln]  ln(1) + ln(2.71828) = 0 + 1 = 1",
-		},
-	},
-}
-
-// buildHelpIndex builds lookup maps from helpTopics at package init.
-var (
-	helpByTopic   = make(map[string]*HelpTopic)     // operator -> topic
-	helpByAlias   = make(map[string]*HelpTopic)     // alias -> topic
-	helpByCat     = make(map[string][]string)       // category -> []operator names
-	categoryOrder []string                          // insertion order of categories
-)
-
-func init() {
-	seenCat := make(map[string]bool)
-	for i := range helpTopics {
-		t := &helpTopics[i]
-		for _, a := range t.Aliases {
-			helpByAlias[a] = t
-		}
-		if !seenCat[t.Category] {
-			seenCat[t.Category] = true
-			categoryOrder = append(categoryOrder, t.Category)
-		}
-		helpByCat[t.Category] = append(helpByCat[t.Category], t.Operator)
-	}
-	// Iterate in reverse so REPL entries (last in slice) take priority
-	// in helpByTopic. This means `help clear` shows the REPL screen-clear
-	// help rather than the RPN variable-clear help.
-	for i := len(helpTopics) - 1; i >= 0; i-- {
-		t := &helpTopics[i]
-		helpByTopic[t.Operator] = t
-	}
-}
-
 // GetHelp returns the formatted help text for a topic.
 // If topic is empty, it returns the general help overview.
 // If topic is "categories", it lists all categories.
diff --git a/internal/repl/help_topics.go b/internal/repl/help_topics.go
new file mode 100644
index 0000000..102f2c1
--- /dev/null
+++ b/internal/repl/help_topics.go
@@ -0,0 +1,489 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2026 Paul Buetow
+
+package repl
+
+type HelpTopic struct {
+	Category    string // e.g. "Arithmetic", "Stack", "Comparison", "Variables", "Hyper", "REPL"
+	Operator    string // the operator or command name (e.g. "+", "help", "rat")
+	Aliases     []string
+	Description string
+	Usage       string // short usage hint
+	Examples    []string
+}
+
+// helpTopics is the single source of truth for all inline help entries.
+// Each entry documents one operator, function, or REPL command with examples.
+var helpTopics = []HelpTopic{
+	// ── REPL commands ──
+
+	{
+		Category:    "REPL",
+		Operator:    "help",
+		Description: "Show help information",
+		Usage:       "help [topic]",
+		Examples: []string{
+			"help              Show general help overview",
+			"help +            Show help for the + operator",
+			"help dup          Show help for dup",
+		},
+	},
+	{
+		Category:    "REPL",
+		Operator:    "clear",
+		Description: "Clear the terminal screen",
+		Usage:       "clear",
+		Examples: []string{
+			"clear",
+		},
+	},
+	{
+		Category:    "REPL",
+		Operator:    "quit",
+		Aliases:     []string{"exit"},
+		Description: "Exit the REPL",
+		Usage:       "quit or exit",
+		Examples: []string{
+			"quit",
+		},
+	},
+	{
+		Category:    "REPL",
+		Operator:    "rpn",
+		Aliases:     []string{"calc"},
+		Description: "Evaluate an RPN (Reverse Polish Notation) expression",
+		Usage:       "rpn <expression>",
+		Examples: []string{
+			"rpn 3 4 +         Evaluate 3 + 4 = 7",
+			"rpn 10 2 /        Evaluate 10 / 2 = 5",
+			"calc 5 3 *        Same as 'rpn 5 3 *'",
+		},
+	},
+	{
+		Category:    "REPL",
+		Operator:    "rat",
+		Description: "Switch between float64 and rational number modes",
+		Usage:       "rat on|off|toggle",
+		Examples: []string{
+			"rat on      Enable rational mode",
+			"rat off     Disable rational mode (float64)",
+			"rat toggle  Toggle between modes",
+		},
+	},
+	{
+		Category:    "REPL",
+		Operator:    "stack",
+		Description: "Show current RPN stack state",
+		Usage:       "stack",
+		Examples: []string{
+			"1 2 3 stack     Show stack: 1 2 3",
+		},
+	},
+
+	// ── Arithmetic operators ──
+
+	{
+		Category:    "Arithmetic",
+		Operator:    "+",
+		Description: "Add two numbers (metric-aware)",
+		Usage:       "a b +",
+		Examples: []string{
+			"3 4 +           3 + 4 = 7",
+			"100Mbps 50 +    100Mbps + 50Mbps = 150Mbps (Cool absorbs metric)",
+		},
+	},
+	{
+		Category:    "Arithmetic",
+		Operator:    "-",
+		Description: "Subtract two numbers (metric-aware)",
+		Usage:       "a b -",
+		Examples: []string{
+			"10 3 -          10 - 3 = 7",
+			"200Mbps 50 -    200Mbps - 50Mbps = 150Mbps",
+		},
+	},
+	{
+		Category:    "Arithmetic",
+		Operator:    "*",
+		Description: "Multiply two numbers",
+		Usage:       "a b *",
+		Examples: []string{
+			"3 4 *           3 * 4 = 12",
+			"100Mbps 2 *     100Mbps * 2 = 200Mbps (Cool preserves metric)",
+		},
+	},
+	{
+		Category:    "Arithmetic",
+		Operator:    "/",
+		Description: "Divide two numbers (a / b)",
+		Usage:       "a b /",
+		Examples: []string{
+			"10 3 /          10 / 3 = 3.333...",
+		},
+	},
+	{
+		Category:    "Arithmetic",
+		Operator:    "^",
+		Description: "Raise to power (a ^ b), result is always unitless",
+		Usage:       "a b ^",
+		Examples: []string{
+			"2 3 ^           2 ^ 3 = 8",
+			"10 0.5 ^        10 ^ 0.5 = sqrt(10) = 3.162...",
+		},
+	},
+	{
+		Category:    "Arithmetic",
+		Operator:    "**",
+		Description: "Raise to integer power (a ** b) using fast binary exponentiation",
+		Usage:       "a b **",
+		Examples: []string{
+			"2 10 **         2 ^ 10 = 1024",
+			"3 6 **          3 ^ 6 = 729",
+		},
+	},
+	{
+		Category:    "Arithmetic",
+		Operator:    "%",
+		Description: "Modulo (remainder of a / b)",
+		Usage:       "a b %",
+		Examples: []string{
+			"10 3 %          10 mod 3 = 1",
+			"7 2 %           7 mod 2 = 1",
+		},
+	},
+	{
+		Category:    "Arithmetic",
+		Operator:    "lg",
+		Description: "Logarithm base 2",
+		Usage:       "a lg",
+		Examples: []string{
+			"8 lg            log2(8) = 3",
+			"1024 lg         log2(1024) = 10",
+		},
+	},
+	{
+		Category:    "Arithmetic",
+		Operator:    "log",
+		Description: "Logarithm base 10",
+		Usage:       "a log",
+		Examples: []string{
+			"100 log         log10(100) = 2",
+			"1000 log        log10(1000) = 3",
+		},
+	},
+	{
+		Category:    "Arithmetic",
+		Operator:    "ln",
+		Description: "Natural logarithm (base e)",
+		Usage:       "a ln",
+		Examples: []string{
+			"2.71828 ln      ln(2.71828) ~= 1",
+			"1 ln            ln(1) = 0",
+		},
+	},
+
+	// ── Comparison operators ──
+
+	{
+		Category:    "Comparison",
+		Operator:    ">",
+		Aliases:     []string{"gt"},
+		Description: "Greater than: pushes true (1) or false (0)",
+		Usage:       "a b >",
+		Examples: []string{
+			"5 3 >           5 > 3 = true (1)",
+			"3 5 >           3 > 5 = false (0)",
+		},
+	},
+	{
+		Category:    "Comparison",
+		Operator:    "<",
+		Aliases:     []string{"lt"},
+		Description: "Less than: pushes true (1) or false (0)",
+		Usage:       "a b <",
+		Examples: []string{
+			"3 5 <           3 < 5 = true (1)",
+			"5 3 <           5 < 3 = false (0)",
+		},
+	},
+	{
+		Category:    "Comparison",
+		Operator:    ">=",
+		Aliases:     []string{"gte"},
+		Description: "Greater than or equal: pushes true (1) or false (0)",
+		Usage:       "a b >=",
+		Examples: []string{
+			"5 5 >=          5 >= 5 = true (1)",
+			"3 5 >=          3 >= 5 = false (0)",
+		},
+	},
+	{
+		Category:    "Comparison",
+		Operator:    "<=",
+		Aliases:     []string{"lte"},
+		Description: "Less than or equal: pushes true (1) or false (0)",
+		Usage:       "a b <=",
+		Examples: []string{
+			"3 3 <=          3 <= 3 = true (1)",
+			"5 3 <=          5 <= 3 = false (0)",
+		},
+	},
+	{
+		Category:    "Comparison",
+		Operator:    "==",
+		Aliases:     []string{"eq"},
+		Description: "Equal: pushes true (1) or false (0)",
+		Usage:       "a b ==",
+		Examples: []string{
+			"5 5 ==          5 == 5 = true (1)",
+			"5 3 ==          5 == 3 = false (0)",
+		},
+	},
+	{
+		Category:    "Comparison",
+		Operator:    "!=",
+		Aliases:     []string{"neq"},
+		Description: "Not equal: pushes true (1) or false (0)",
+		Usage:       "a b !=",
+		Examples: []string{
+			"5 3 !=          5 != 3 = true (1)",
+			"5 5 !=          5 != 5 = false (0)",
+		},
+	},
+
+	// ── Stack operators ──
+
+	{
+		Category:    "Stack",
+		Operator:    "dup",
+		Description: "Duplicate the top stack value",
+		Usage:       "a dup",
+		Examples: []string{
+			"5 dup           Stack: 5 5",
+			"3 dup dup       Stack: 3 3 3",
+		},
+	},
+	{
+		Category:    "Stack",
+		Operator:    "swap",
+		Description: "Swap the top two stack values",
+		Usage:       "a b swap",
+		Examples: []string{
+			"1 2 swap        Stack: 2 1",
+		},
+	},
+	{
+		Category:    "Stack",
+		Operator:    "pop",
+		Description: "Remove and discard the top stack value",
+		Usage:       "pop",
+		Examples: []string{
+			"1 2 3 pop       Stack: 1 2",
+		},
+	},
+	{
+		Category:    "Stack",
+		Operator:    "d",
+		Description: "Pop a symbol from stack and delete that variable",
+		Usage:       ":x d",
+		Examples: []string{
+			":x d            Delete variable x",
+		},
+	},
+	{
+		Category:    "Stack",
+		Operator:    "show",
+		Aliases:     []string{"showstack", "print"},
+		Description: "Display the current stack contents",
+		Usage:       "show",
+		Examples: []string{
+			"1 2 3 show      Prints: 1 2 3",
+			"show            Prints: Stack is empty",
+		},
+	},
+
+	// ── Variable operators ──
+
+	{
+		Category:    "Variables",
+		Operator:    ":=",
+		Description: "Assign value to variable (name on bottom, value on top)",
+		Usage:       ":name value :=",
+		Examples: []string{
+			":x 5 :=         Set variable x to 5",
+			":y 3.14 :=      Set variable y to 3.14",
+		},
+	},
+	{
+		Category:    "Variables",
+		Operator:    "=:",
+		Description: "Assign value to variable (value on bottom, name on top)",
+		Usage:       "value :name =:",
+		Examples: []string{
+			"5 :x =:         Set variable x to 5",
+		},
+	},
+	{
+		Category:    "Variables",
+		Operator:    "vars",
+		Description: "List all defined variables and their values",
+		Usage:       "vars",
+		Examples: []string{
+			"vars            List all variables",
+		},
+	},
+	{
+		Category:    "Variables",
+		Operator:    "clear",
+		Description: "Clear all user-defined variables",
+		Usage:       "clear",
+		Examples: []string{
+			"clear           Remove all variables",
+		},
+	},
+	{
+		Category:    "Variables",
+		Operator:    "convert",
+		Description: "Convert a value to a target metric (@X syntax)",
+		Usage:       "value @target convert",
+		Examples: []string{
+			"100Mbps @bps convert    Convert 100Mbps to bps",
+		},
+	},
+
+	// ── Constants ──
+
+	{
+		Category:    "Constants",
+		Operator:    "constants",
+		Description: "List all available constants",
+		Usage:       "constants",
+		Examples: []string{
+			"constants       List all built-in constants",
+		},
+	},
+	{
+		Category:    "Constants",
+		Operator:    "clearconstants",
+		Description: "Reset all constants to built-in defaults",
+		Usage:       "clearconstants",
+		Examples: []string{
+			"clearconstants  Reset constants",
+		},
+	},
+
+	// ── Hyper (n-ary) operators ──
+
+	{
+		Category:    "Hyper",
+		Operator:    "[+]",
+		Description: "Add all stack values together (n-ary)",
+		Usage:       "a b c [+] ...",
+		Examples: []string{
+			"1 2 3 [+]       1 + 2 + 3 = 6",
+			"10 20 30 40 [+] 100",
+		},
+	},
+	{
+		Category:    "Hyper",
+		Operator:    "[-]",
+		Description: "Subtract all stack values left-associative (n-ary)",
+		Usage:       "a b c [-] ...",
+		Examples: []string{
+			"10 3 2 [-]      10 - 3 - 2 = 5",
+		},
+	},
+	{
+		Category:    "Hyper",
+		Operator:    "[*]",
+		Description: "Multiply all stack values together (n-ary)",
+		Usage:       "a b c [*] ...",
+		Examples: []string{
+			"2 3 4 [*]       2 * 3 * 4 = 24",
+		},
+	},
+	{
+		Category:    "Hyper",
+		Operator:    "[/]",
+		Description: "Divide all stack values left-associative (n-ary)",
+		Usage:       "a b c [/] ...",
+		Examples: []string{
+			"100 2 5 [/]     100 / 2 / 5 = 10",
+		},
+	},
+	{
+		Category:    "Hyper",
+		Operator:    "[^]",
+		Description: "Power all stack values left-associative (n-ary)",
+		Usage:       "a b c [^] ...",
+		Examples: []string{
+			"2 3 2 [^]       2 ^ 3 ^ 2 = 8",
+		},
+	},
+	{
+		Category:    "Hyper",
+		Operator:    "[%]",
+		Description: "Modulo all stack values left-associative (n-ary)",
+		Usage:       "a b c [%] ...",
+		Examples: []string{
+			"100 10 3 [%]    100 % 10 % 3 = 1",
+		},
+	},
+	{
+		Category:    "Hyper",
+		Operator:    "[lg]",
+		Description: "Sum of log2 of all stack values (n-ary)",
+		Usage:       "a b [lg] ...",
+		Examples: []string{
+			"2 4 [lg]        log2(2) + log2(4) = 1 + 2 = 3",
+		},
+	},
+	{
+		Category:    "Hyper",
+		Operator:    "[log]",
+		Description: "Sum of log10 of all stack values (n-ary)",
+		Usage:       "a b [log] ...",
+		Examples: []string{
+			"10 100 [log]    log10(10) + log10(100) = 1 + 2 = 3",
+		},
+	},
+	{
+		Category:    "Hyper",
+		Operator:    "[ln]",
+		Description: "Sum of natural log of all stack values (n-ary)",
+		Usage:       "a b [ln] ...",
+		Examples: []string{
+			"1 2.71828 [ln]  ln(1) + ln(2.71828) = 0 + 1 = 1",
+		},
+	},
+}
+
+// buildHelpIndex builds lookup maps from helpTopics at package init.
+var (
+	helpByTopic   = make(map[string]*HelpTopic) // operator -> topic
+	helpByAlias   = make(map[string]*HelpTopic) // alias -> topic
+	helpByCat     = make(map[string][]string)   // category -> []operator names
+	categoryOrder []string                      // insertion order of categories
+)
+
+func init() {
+	seenCat := make(map[string]bool)
+	for i := range helpTopics {
+		t := &helpTopics[i]
+		for _, a := range t.Aliases {
+			helpByAlias[a] = t
+		}
+		if !seenCat[t.Category] {
+			seenCat[t.Category] = true
+			categoryOrder = append(categoryOrder, t.Category)
+		}
+		helpByCat[t.Category] = append(helpByCat[t.Category], t.Operator)
+	}
+	// Iterate in reverse so REPL entries (last in slice) take priority
+	// in helpByTopic. This means `help clear` shows the REPL screen-clear
+	// help rather than the RPN variable-clear help.
+	for i := len(helpTopics) - 1; i >= 0; i-- {
+		t := &helpTopics[i]
+		helpByTopic[t.Operator] = t
+	}
+}