Failed to update setting: invalid max history

Error message

Failed to update setting: invalid max history '{value}'. Expected a positive number.

What it means

Settings::set parses the `max_history`/`history` value as usize via str::parse; a parse failure produces this error. The message says 'positive number' though the type also accepts 0 — only non-numeric (or, on some platforms, overflowingly large) strings fail.

Solutions

Pass a plain non-negative integer with no units or separators, e.g. `100`.
Strip whitespace; str::parse does not trim trailing text.
On 32-bit builds, keep the value within u32 range to avoid overflow rejections.

Example fix

// before
settings.set("max_history", "10,000")?;
// after
settings.set("max_history", "10000")?;

Defensive patterns

Strategy: validation

Validate before calling

fn valid_max_history(v: &str) -> bool {
    v.trim().parse::<usize>().is_ok()
}

Try / catch

match value.trim().parse::<usize>() {
    Ok(n) => settings.set("max_history", &n.to_string())?,
    Err(_) => eprintln!("max_history must be a plain positive integer"),
}

Prevention

Parse numeric user input in the wrapper first; reject units and separators.
Serialize numbers with .to_string(), never locale formatting.
Clamp values in your UI before writing.

When it happens

Trigger: Settings::set("max_history", v) where v is not a valid usize literal — e.g. `history fifty`, `history 1000 entries`, `history -5`, or a value exceeding usize::MAX on 32-bit targets.

Common situations: Scripted /config commands passing prose or units ('5000 lines'), locales formatting numbers with separators ('10,000'), or negative numbers.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of Hmbown/CodeWhale@73e0f67d83 (2026-09-22). Data as JSON: /api/errors/4d841430392fdefe. Report an issue: GitHub.

Appendix: source

Thrown at crates/tui/src/settings.rs:1738

                        "Failed to update setting: invalid cost currency '{value}'. Expected: usd, cny, rmb, yuan."
                    );
                };
                self.cost_currency = match currency {
                    crate::pricing::CostCurrency::Usd => "usd",
                    crate::pricing::CostCurrency::Cny => "cny",
                }
                .to_string();
            }
            "max_history" | "history" => {
                let max: usize = value.parse().map_err(|_| {
                    anyhow::anyhow!(
                        "Failed to update setting: invalid max history '{value}'. Expected a positive number."
                    )
                })?;
                self.max_input_history = max;
            }
            "default_model" | "model" => {
                anyhow::bail!(
                    "Model defaults belong to config.toml. Use /model and choose Remember as my default, or /config model <id> --save."
                );
            }
            "reasoning_effort" | "effort" => {
                self.reasoning_effort = normalize_reasoning_effort_setting(value)?;
            }
            "permission_posture" | "permissions" => {
                self.permission_posture = normalize_permission_posture(value);
                if self.permission_posture.is_none() {
                    anyhow::bail!(
                        "Failed to update setting: invalid permission posture '{value}'. Expected: ask, auto-review, or full-access."
                    );
                }
            }
            "sandbox_mode" | "sandbox" | "filesystem_sandbox" => {
                self.sandbox_mode = normalize_sandbox_mode(value);
                if self.sandbox_mode.is_none() {
                    anyhow::bail!(

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