Update context header per discussion resolution

Author: djbqrex

standards/request-response.md

@@ -504,15 +504,19 @@ Sps-Cors-Error: bad origin
     - __prod__ - Well-known value used to represent production customer configuration and can be supported as a static mode in some legacy services without full dynamic support. Usage of dynamically named configuration sets is preferred. When no request or response header is provided for `Sps-Execution-Context` this is interpreted as the default value.
 - An invalid or unsupported header value provided **MUST** result in a `400 - Bad Request` following standard [error format](errors.md#400-bad-request).
 - The header value **MUST** be at minimum 1 character in length and  **MUST NOT** exceed a maximum length of 100 characters.
-- The header value **MUST** be case-insensitive.
-- The header value **MUST** conform to: `[A-Za-z0-9_-]`.
-  - It **MUST** only contain ASCII letters (A–Z, a–z), digits (0–9), underscore (`_`), or hyphen (`-`).
+- The header value **MUST** be lowercase.
+- The header value **MUST** conform to: `[a-z0-9_-]`.
+  - It **MUST** only contain ASCII lowercase letters (a–z), digits (0–9), underscore (`_`), or hyphen (`-`).
   - It **MUST NOT** contain accented/diacritic or non-ASCII characters.
 - The header value **SHOULD** contain human-readable tag for the context.
 - The original requested header value **SHOULD** be propagated to any outgoing requests to retain the context for downstream usage.
 - The header **MUST** be supplied in the response for every request containing the header, and match the original requested value.
 - The header **SHOULD** be supplied in the response for every request in general, if applicable to the API, even if just defaulting to __prod__.
 
+```note
+The allowed character set is intentionally conservative and may expand in the future. Implementations should avoid hard-coding assumptions and be prepared for a broader set if the standard is updated.
+```
+
 **Example(s)**:
 
 ```
@@ -523,7 +527,7 @@ Sps-Execution-Context: customer-testing
 Sps-Execution-Context: example-customer-configuration
 Sps-Execution-Context: example_customer_config
 Sps-Execution-Context: release-2025-10-07
-Sps-Execution-Context: JIRA-007-something-descriptive
+Sps-Execution-Context: jira-007-something-descriptive
 
 // INCORRECT
 Sps-Execution-Context:                  // values must be at least a character long.
@@ -532,6 +536,7 @@ Sps-Execution-Context: customer testing // space not allowed
 Sps-Execution-Context: example@config   // '@' not allowed
 Sps-Execution-Context: preprod\n        // control/newline not allowed
 Sps-Execution-Context: Français         // désolé, ASCII-only, s'il vous plaît
+Sps-Execution-Context: JIRA-007         // uppercase letters not allowed; use lowercase
 ```
 
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