Cache TLS 1.2 client sessions only after the server Finished verifies

[gasbytes]

Description

The client cached its session and ticket before verifying the server Finished,
so a failed handshake left a resumable session behind (RFC 5246 Section 7.2.2).
Caching moves to DoFinished(); the server path is unchanged.

Testing

Added three regression tests to also cover the edge cases: ticket dropped on a bad Finished, cached after a good one, and preserved across a resumption with an empty NewSessionTicket.

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[Copilot]

🟡 Changes recommended

The new “drop ticket” path on Finished verification failure clears logical state but can retain dynamically allocated ticket buffers, which can unnecessarily hold memory after a failed handshake.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR fixes TLS 1.2 client session-ticket caching semantics so that a client session/ticket is only cached after the server Finished has been verified, preventing resumable sessions from being left behind after failed handshakes (per RFC 5246 §7.2.2).

Changes:

• Move TLS 1.2 client session caching to DoFinished() (post server-Finished verification); keep server caching behavior in SendFinished().
• Clear unverified session tickets when Finished verification fails.
• Add regression tests covering: bad Finished dropping tickets, successful Finished caching, and empty-renewal tickets preserving cached entries.

File summaries

File	Description
tests/api/test_tls.h	Registers three new TLS 1.2 session-ticket caching regression tests in the API test suite.
tests/api/test_tls.c	Implements regression tests for caching only after verified Finished and for preserving/dropping tickets in edge cases.
src/internal.c	Shifts client-side caching to post-Finished verification, drops unverified tickets on Finished failure, and avoids caching on empty ticket renewals.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

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[github-actions]

MemBrowse Memory Report

gcc-arm-cortex-m3

• FLASH: .text +16 B (+0.0%, 125,763 B / 262,144 B, total: 48% used)

gcc-arm-cortex-m4-openssl-compat

• FLASH: .text +128 B (+0.0%, 783,004 B / 1,048,576 B, total: 75% used)

gcc-arm-cortex-m4-pq

• FLASH: .text +64 B (+0.0%, 301,704 B / 1,048,576 B, total: 29% used)

gcc-arm-cortex-m4-rsa-only

• FLASH: .text +192 B (+0.1%, 332,576 B / 1,048,576 B, total: 32% used)

gcc-arm-cortex-m4-tls13

• FLASH: .text +64 B (+0.0%, 242,191 B / 262,144 B, total: 92% used)

gcc-arm-cortex-m7-pq

• FLASH: .text +64 B (+0.0%, 302,600 B / 1,048,576 B, total: 29% used)

gcc-arm-cortex-m7-tls13

• FLASH: .text +64 B (+0.0%, 242,255 B / 262,144 B, total: 92% used)
  No memory changes detected for:
• gcc-arm-cortex-m0plus
• gcc-arm-cortex-m4
• gcc-arm-cortex-m4-baremetal
• gcc-arm-cortex-m4-crypto-only
• gcc-arm-cortex-m4-dtls13
• gcc-arm-cortex-m4-min-ecc
• gcc-arm-cortex-m4-pkcs7
• gcc-arm-cortex-m4-sp-math
• gcc-arm-cortex-m4-tls12
• gcc-arm-cortex-m7
• linuxkm-pie
• linuxkm-standard
• stm32-sim-stm32h753