[fakedev9999]

What

• Add optional watch publishers to SP1Context for the latest 2 KiB guest stdout and stderr snapshots.
• Forward portable output at the minimal VM write boundary and native output through the child stderr drain.
• Restore SDK stdout and stderr capture methods and test both execution paths.

Why

V6 callers need a panic summary and location after execution when prover logs are unavailable.

Validation

• cargo check --release --all-targets --all-features --tests
• cargo check --release --workspace --all-targets --no-default-features
• cargo clippy --release --all-features --all-targets -- --deny warnings --allow incomplete-features
• Focused snapshot-bound, writer compatibility, runner panic, SDK panic, and SDK stdout tests
• cargo fmt --all -- --check

Notes

• The caller keeps the receiver alive and clones its final value after execution. The native runner joins its stderr drain before it returns.
• A long-lived receiver borrow can briefly delay the publisher. The intended post-execution read does not hold a borrow during execution.
• This adds a field to public SP1Context. Known Succinct callers use its builder or ..Default; unknown exhaustive external literals need an update.
• This replaces feat(executor): capture bounded guest stderr tail in ExecutionReport #2859 without changing ExecutionReport, JIT state, or runner bincode.
• sp1-cluster consumption remains a follow-up.

[github-actions]

Test	Old	New	Diff
secp256k1_program_test_recover_rand_lte_100	5527378	5528732	0.0245 %
k256_test_point_ops_edge_cases	32628	32628	0.0000 %
curve25519_dalek_test_decompressed_noncanonical	7851	7851	0.0000 %
k256_test_recover_rand_lte_100	4568789	4575033	0.1367 %
curve25519_dalek_ng_test_zero_msm	125094	125094	0.0000 %
secp256k1_program_test_verify_v0_30_0_rand_lte_100	17092578	17094126	0.0091 %
bn_test_bn_test_g1_add_100	998846	998825	-0.0021 %
curve25519_dalek_test_zero_msm	83313	83313	0.0000 %
curve25519_dalek_test_decompressed_expected_value	4561440	4561440	0.0000 %
bls12_381_tests_test_inverse_fp_100	1205483	1205483	0.0000 %
curve25519_dalek_test_add_then_multiply	2809102	2943631	4.7890 %
k256_test_recover_high_hash_high_recid	2113029	2307240	9.1911 %
k256_test_verify_rand_lte_100	11722515	11765823	0.3694 %
p256_test_recover_pubkey_infinity	97102	97102	0.0000 %
curve25519_dalek_test_ed25519_verify	13355529	13355368	-0.0012 %
bn_test_bn_test_g1_msm_edge	411941	411941	0.0000 %
bn_test_bn_test_g1_mul_zero	48333	48333	0.0000 %
bn_test_bn_test_fq_partial_ord	186343	186343	0.0000 %
bls12_381_tests_test_bls_add_100	10376534	10376534	0.0000 %
bls12_381_tests_test_sqrt_fp2_100	2001746	1915292	-4.3189 %
curve25519_dalek_test_zero_mul	71730	71730	0.0000 %
bls12_381_tests_test_sqrt_fp_100	864870	859348	-0.6385 %
sha_test_sha2_v0_10_6_expected_digest_lte_100_times	1356096	1358578	0.1830 %
sha_test_sha3_expected_digest_lte_100_times	1198982	1198887	-0.0079 %
bn_test_bn_test_fr_inverse_100	822631	822631	0.0000 %
secp256k1_program_test_verify_rand_lte_100	17077199	17068890	-0.0487 %
keccack_test_expected_digest_lte_100	1722106	1723843	0.1009 %
curve25519_dalek_ng_test_zero_mul	107709	107709	0.0000 %
k256_test_schnorr_verify	5718600	5715146	-0.0604 %
rustcrypto_bigint_test_bigint_mul_mod_special	1785802	1785802	0.0000 %
secp256k1_program_test_recover_v0_30_0_rand_lte_100	5478770	5478255	-0.0094 %
bn_test_bn_test_fq_sqrt_100	804031	804031	0.0000 %
sha_test_sha2_v0_9_9_expected_digest_lte_100_times	1269571	1265192	-0.3449 %
bls12_381_tests_test_bls_double_100	6310230	6310230	0.0000 %
bn_test_bn_test_g1_double_100	735539	735518	-0.0029 %
bn_test_bn_test_g1_add_neg	299549	299549	0.0000 %
k256_test_recover_pubkey_infinity	101996	101996	0.0000 %
rustcrypto_bigint_test_bigint_mul_add_residue	1747305	1747305	0.0000 %
sha_test_sha2_v0_10_9_expected_digest_lte_100_times	1353502	1358685	0.3829 %
curve25519_dalek_ng_test_add_then_multiply	4061958	4293952	5.7114 %
p256_test_recover_rand_lte_100	15773619	15816774	0.2736 %
sha_test_sha2_v0_10_8_expected_digest_lte_100_times	1354451	1360610	0.4547 %
bls12_381_tests_test_inverse_fp2_100	2230063	2230063	0.0000 %
bn_test_bn_test_fq_inverse_100	805631	805631	0.0000 %
curve25519_dalek_ng_test_decompressed_noncanonical	195347	195347	0.0000 %
rust_crypto_rsa_test_pkcs_verify_100	29251186	29043486	-0.7101 %
p256_test_recover_high_hash_high_recid	4318627	6548675	51.6379 %
p256_test_verify_rand_lte_100	11998111	11966139	-0.2665 %